"Robert Smithson would always say to me, 'David, you're a smart cookie, why are you still painting?'" recalls David Diao, who at 72 is still painting. This commitment to canvas is, in fact, a rare constant in Diao's career, now in its fifth decade. But he's not a chauvinist about the medium: If anything, the body of work he has produced over this period, spanning large-scale abstraction, Conceptualism, and a turn toward visual and textual citation, represents less the efforts of a hermetic allegiance than it does working through the intellectual history of painting and visual art in the last half-century. Since the mid 1980s, when he abandoned pure formalism for a marriage of form and content, Diao has parsed the legacies of modernism—in particular, the painters Barnett Newman and Kazimir Malevich and the architects Philip Johnson and Konstantin Melnikov—just as he has rigorously dissected his own subjectivity as an artist and a Chinese immigrant. In two marathon conversations with Modern Painters over the course of the past year, Diao considered his career as he prepared for two retrospectives: the first, "Front to Back," at the Aldrich Contemporary Art Museum in Connecticut, ran July 13 to September 21, 2014; the other, a much larger exhibition of over 90 works, opens this month at the Ullens Center for Contemporary Art in Beijing.

Diao speaks with the engrossing cadence of a conversational story-teller, his self-deprecating and professorial mien betraying no hints of the geographic instability of his early youth. He joined his father in New York City in 1955 at age 12, following an escape from Chengdu, the city of his birth, to Hong Kong, in 1949, on the eve of the formation of the Maoist state. After studying philosophy at Kenyon College in Ohio, he returned to New York to attend Cooper Union. Soon he began working as an assistant at the Kootz Gallery during the day, handling art and doing odd jobs for Samuel Kootz. "I stopped going to Cooper Union after the first semester, because I felt it was taking away from my studio time," he says. In 1965 Diao settled into a 22-by-147-foot loft on Canal Street, and the following year, when the Kootz Gallery closed, he went freelance, working as a handler and installer, even storing artworks for various galleries in his cavernous apartment. And so he came to share the space with works like Franz Kline's monumental Cardinal, a painting he would later reference in his own work (the floor plan of that loft, too, would eventually surface in Diao's art). His coffee table for some time was a Tony Smith Corten steel box. At one point the Fischbach Gallery, which owned the work, instructed him to relocate it to his fire escape for a little patina development. "They didn't seem to care about insurance," Diao says.

During a stint as a preparator at the Guggenheim, he "lucked into" installing Barnett Newman's The Stations of the Crossin 1966. Newman would later become the subject of one of Diao's longest-running series, cataloguing the late artist's output in a 1991 painting titled Barnett Newman, the Paintings in Scale. That work reappeared as the subject of Home Again, 2013, which chronicled Diao's eventual repurchase of his 1991 work at auction in Hong Kong. (Home Again was also one of two of his paintings included by Michelle Grabner in the 2014 Whitney Biennial.) Referentiality and self-referentiality of this type, the formal and conceptual digestion of his modernist heroes and his own narrative, had not yet dawned in Diao's formative New York of the 1960s. Like many artists of this period, he eschewed a traditional art education for the company of his peers, pursuing graduate study at Max's Kansas City, the Park Avenue South bar that would become his haunt when the painter Michael Goldberg brought him there shortly after it opened in 1965.

"We all wanted to do the next thing after Frank Stella. Looking back, we thought about painting as finding some system, or finding some plan, and then executing it repeatedly," Diao notes of his early preoccupations. Indeed, before his turn away from pure abstraction, he was a dyed-in-the-wool formalist, though conceptual inclinations shone through from the beginning. He began his career making large "square" paintings with diagonal lines, influenced by Ad Reinhardt, an example of which he showed at the cooperative Park Place Gallery in 1967, which evolved into an interest in process and material. This manifested itself in his first solo exhibition at Paula Cooper Gallery, in 1969. He had met Cooper at Park Place, where she was the gallery director, and eventually joined her founding roster, becoming one of the first artists she presented in a solo exhibition. "The show was called 'Sheetrock,'" Diao says, "and one piece was five standard panels of Sheetrock, four by eight feet, which I actually went to several different lumberyards to get, because I discovered there were subtle differences in color, to the point that some are pinkish while others are greenish."

"I remember the sculpture very, very well," Cooper recalled on a recent afternoon. "It was very much his own work. It was quite elegant, and I wouldn't describe a lot of work at that time as elegant, exactly. It didn't have that rigorous kind of purity that a lot of work had, and it wasn't funky. People were very involved with material, so 'Sheetrock' was a part of that, but I never got the feeling that he was interested in material or process in the way that artists who were really interested in the properties of material were." In addition to the Sheetrock piece, Diao showed a hollow Homasote box that was an explicit reference to the Tony Smith with which he had cohabi-tated, but worked through in a lightweight paper-based material and sanded for a suedelike finish. "It had this really soft, gray surface. There was a fineness about David's work. It was different from other people's in that way," Cooper said.

"One of the reasons I was drawn to process art," Diao says, "is that it's a way not to keep anything mysterious. If what you're doing can be reconstituted by the viewer, you're dealing the viewer into the image. Anyone using the same instrument could do the same job." This ethos followed Diao into large-scale abstraction and large-scale success. He sold strongly in early shows, catching the attention of the collector Larry Aldrich, who included Diao in "Young Lyrical Painters," his 1969 Art in America article on lyrical abstraction. But Diao did not buy the categorization: "Though I didn't speak to him personally, I loudly said that I don't think my work is lyrical abstrac-tion." For Diao, even at this early stage, lyrical abstraction implied too much autonomy, relying on a sort of mysticism that his interest in process simply did not allow, even if the results were similar enough to fool Aldrich. The marks that Aldrich had misdiagnosed as lyrical were in fact highly procedural exercises in one-to-one mark-making: Diao would use found cardboard rollers, some five feet wide, as squeegees, a method that has come to be associated with Gerhard Richter. Word of the artist's objection traveled, and when Aldrich put together his "Lyrical Abstraction" exhibition, which went from his eponymous Connecticut museum to New York's Whitney Museum in 1970 and '71, the artist was not included. Diao was "both happy and unhappy" about this correction—intellectual honesty had come at the cost of valuable institutional recognition.

Though his second exhibition at Paula Cooper, in 1970, was a success, with work acquired by Aldrich and others, it would also be his last at the gallery. After a misstep involving a sale done with an outside dealer, Diao would soon find himself off the roster, landing a short while later at Reese Palley, a well-funded upstart founded by an Atlantic City entrepreneur. "A little while after that, Reese Palley offered me a big one-person show, and that was probably, to my mind, the biggest mistake I ever made, because Reese Palley closed and Cooper went on to become a major gallery," Diao says. Palley's gallery was a flash in the pan, employing the bellicose critic Dave Hickey as director and showing a number of prominent artists of that moment, including Jennifer Bartlett and Yoko Ono. But despite this setback, the early shows earned Diao some momentum: In 1969 alone he managed to show with Peter Young at Leo Castelli Gallery and with Brice Marden at Carmen Lamanna Gallery in Toronto; and in 1972 he appeared alongside Cy Twombly in a Hampshire College exhibition.

As Diao's market fortunes waned, he immersed himself in intellectual life, joining the faculty of the Whitney Independent Study Program (ISP) in 1970, an involvement that would last until 2000. He also taught at the School of Visual Arts, where he filled in for an ill Eva Hesse, and at Yale and Cooper Union. Though intellectually productive—through teaching, particularly at the ISP, the Frankfurt School entered into his thought—the mid to late 1970s was not a prolific period for Diao, which allowed him to explore the combination of "rationale with immediacy" at length. "It happened to be a time when there wasn't much interest in my work, so I had the leisure to focus on the same paintings a very long while. Between around '74 and '82, there were probably about 10 paintings I could stand behind," Diao says. In 1974 he decamped from SoHo and obtained a lease on a loft building on Franklin Street in Tribeca, splitting it floor by floor with ISP colleagues Ron Clark and Yvonne Rainer. Today only Diao remains in the building, sharing the elegant, modernist furniture–strewn space with his longtime partner, artist Maureen Connor, whom he calls his "most honest and critical friend."

By the dawn of the next decade, however, he felt stuck, and escaped to Paris in 1983. "This was the dead of winter for me in terms of work, when I had no idea what to do," Diao says. But soon a breakthrough arrived, care of Kazimir Malevich's 1915 debut of his Suprematist paintings. "I could use the Malevich to allude to something bigger, because it does have this resonance as an Urmoment of abstraction, and what could be better than to point to that, and in a way try to steal its thunder? And that was a big opening for me. Once I realized I could do that, the sterility of the conventions seemed to break open somehow," Diao explains. Thus, his introduction of silkscreen and vinyl onto the painted canvas: a citational strategy that allowed content—external images and symbols—to come into painterly congress.

The first painting from his Malevich series, On Our Land, executed in the fall of 1984, juxtaposed an inverted black Suprematist triangle with a Palestinian flag picked up at a march on Fifth Avenue. The formal doubling echoed Diao's own sense of territorial dispossession relative to the great modernists, relating the land Palestinians sought to regain and, as the artist put it, "the terrain of this critical art that I love so much." It was at this point that his current New York gallerist, Magda Sawon of Postmasters, added Diao to her inaugural stable of artists. "She rescued me from the gutter," Diao offers, the hyperbole and gratitude in his pronouncement lingering over the bowl of bright, early-season strawberries he has set between us.

Underneath the crimson expanse of Diao's later Barnett Newman painting in the back room of Postmasters, Sawon recalled her 1984 studio visit with Diao. "Going back to 1984, that Malevich group of work was for me fascinating and very understandable, perhaps because I had an art historical background and had come from Eastern Europe, so there were these two kinds of connectors that—on top of everything else—allowed me to embrace and understand the work," Sawon says. She ended up enlisting him for a solo exhibition in 1985.

"That show was his reemergence on the scene, and it was very successful, it was a very serious proposition," she adds. Prominent collectors like Barbara and Eugene Schwartz purchased works, and it was widely reviewed, earning a feature in Art in America titled "Diaorama," by Stephen Westfall.

Three decades on, Diao is the longest-tenured artist on the Postmasters roster, and with the small retrospective exhibition at the Aldrich museum last year, even his earlier, large-format abstractions are undergoing something of a renaissance. "We have at this point a serious reawakening in his vintage work," Sawon said. Read through Diao's autobiographical paintings chronicling his sales (Sales, 1991) and exhibitions (the three-panel Résumé, 1991), this resurgence of interest alights upon an artist whose subtle modesty, his status as a stalwart observer, has been definitive of his practice. "Most artists," Diao deadpans, "are not like Brice Marden; most artists are like me." In one especially playful work, Synecdoche, 1993, a Gerhard Richter catalogue essay by Benjamin H.D. Buchloh is annotated and pasted over: Each instance of Richter's name is crossed out and replaced with Diao's, and each "squeegee" painting is pasted over with an earlier work in the same style from Diao. In conversation, Diao tells me that he considered modifying Buchloh's initials to read "PhD," a reference to the critic's delayed dissertation. Call it critical historicism, or insider-outsider pranksterism.

As Diao continued to tackle successive histories, and historicities, through the end of the '80s and into the following decades, the teaching appointments continued to come in. At Hampshire College in 1996 he met Walid Raad, and the pair struck up a friendship that would eventually give rise to a 2012 joint exhibition at Paula Cooper, where Raad is on the roster. "I came to be attracted to his use of graphic lines, whether from architectural drawings or plans, and of other lines borrowed from institutional documents, as well as his use of words and his choice of colors," Raad says. "I always wondered where his lines and colors originated, and the relations he sets up between the final lines on his canvas and their original referents. Moreover, I wondered why he needed these 'borrowed' lines and colors to paint, to make paintings per se. It is clear that David has been deeply affected by certain forms and concepts from modern art and architecture, mostly Western modernism, so much so that he was unable to paint unless he went through them again—not in the sense of repeating them, nor adapting them, but in some 'repeating for the first time again' kind of gesture. This is the type of gesture that I am drawn to time and again in his works." For her part, Cooper was glad that Raad brought in Diao for the exhibition. "It was very nice to see him again. I was impressed with the work," she said.

It was also in the 1990s and 2000s that Diao came into making work about his Asian-American identity, using an image of Bruce Lee in a simulated museum exhibition invitation in 1994's Carton d'invitation, for example, or exploring his family origins in China with a 2007–08 series on the layout of his ancestral Da Hen Li house in Chengdu. As he moves through the archives of modern art and architecture and into the history, memories, and sentiments of his own identity, Diao's clinical style does not seem to dissolve. "Identity politics entered the picture in the 1990s, and I had to respond to it," he says, adding, half jokingly, that he was "dragged kicking and screaming. I was very happy dealing with high modernism." This heterodox willingness to embrace and work through different positions has resulted in a diffractive body of scholarship and criticism on his work, from Aldrich's rebuked "lyrical abstraction" thesis to Žižekian racial theory (Paul A. Anderson in Third Text, Winter 1995–96) to data visualization (Michael Corris in the Ullens catalogue).

Out of this relentless inventiveness emerges the need for a comprehensive assessment of Diao's work, a role the hardcover Ullens Center catalogue intends to occupy. Superficially, the Ullens retrospective is a sort of geographic return to the origin for an artist who has little interest in the point of origin as such: "I honestly don't see how my work could register in China. Things are changing, though, and younger artists are influenced by what's happening elsewhere," Diao says. Ullens curator and director Philip Tinari acknowledges that this exhibition is not a homecoming but an invitation. "Hopefully, it can bring out the best in both contexts. It's certainly not an attempt to 'claim' him for China. But his is a body of work that is more globally relevant than ever, particularly here and now."