Brent Sikkema, an influential and well respected New York City gallerist, was found dead on Jan. 15 in an apartment he owned in Rio de Janeiro. He was 75.

The Brazilian police said that he had apparently been stabbed multiple times, and that an investigation was ongoing. A suspect was arrested on Thursday.

As the founder of what became the Sikkema Jenkins & Co. gallery in Manhattan’s Chelsea arts district, Mr. Sikkema discovered, guided, exhibited and sold a diverse and notably international rotation of distinguished artists whose work married bright, accessible colors to substantive subjects like memory, race and identity.

Sikkema Jenkins represented artists at every stage of their careers — from Sheila Hicks, a long-established pioneer of textile art, to Louis Fratino, a young figurative painter — and in every medium, from the politically inflected sculptor William Cordova to the estate of the choreographer Trisha Brown. Some artists inevitably moved on to larger galleries. But a tight core of loyalists, most notably Vik Muniz, Arturo Herrera and Kara Walker, remained with Mr. Sikkema for decades as they built their careers together.

“Brent Sikkema and I had a personal connection that went well beyond that of gallery director and exhibiting artist,” Ms. Walker said in a statement. “He was a nurturing, protective figure to me when I was a quite young upstart. He saw in me something beyond what either of us could fully articulate, but I think we brought out the best in each other.”

Writing about Mr. Sikkema on Instagram, Mr. Muniz, a photographer who was born in São Paulo and now has homes in New York and Rio, said, “I have spent more than 30 years trying to pointlessly emulate his juggling of fearlessness, kindness and sophistication.”

In recent years Mr. Sikkema had been somewhat less engaged with the gallery’s day-to-day operations as he spent more time in Brazil, where he was seeking residency and where several of his artists lived. But the institution, which he had built around his own taste and judgment, continued to touch artists like the painter Brenda Goodman, who began showing with Sikkema Jenkins in 2019 — but who had aspired to do so for many years before that.

“I first moved to New York in 1976,” she said in an interview, and since the moment Sikkema Jenkins opened, “that was my dream gallery.”

Brent Fay Sikkema was born on Aug. 13, 1948, in Morrison, Ill., the younger of two children of Dwaine Louis Sikkema and Emily (Howe) Sikkema. For a time his parents owned and operated a tavern in Morrison.

Mr. Sikkema and his husband, Daniel (Garcia) Sikkema, were in the midst of a divorce. He is also survived by their son, Lucas Sikkema.

Mr. Sikkema earned a B.F.A. degree in 1970 and an M.F.A. in 1971 from the San Francisco Art Institute, where he studied filmmaking and photography. He won grants as a photographer from the National Endowment for the Arts in 1975 and 1979. As late as 1990, when he had a solo show at the Thomas Segal Gallery in Boston, he was still making photographs of his own, using multiple exposures to create black-and-white prints full of art-historical references.

But he also began working with other people’s art right out of school, as director of traveling exhibitions and then director of exhibitions at the nonprofit Visual Studies Workshop in Rochester, N.Y. In 1976 he moved to the Vision Gallery in Boston, which handled 19th- and 20th-century photography and listed many museums among its clients. By 1980, he had become the gallery’s owner.

(He was also briefly married to Mary Pratt, Vision’s founder; that early marriage was the second of two that ended in divorce.)

In 1989, he staged his first show in New York under the name Brent Sikkema Fine Art. Two years later he opened a permanent space in SoHo that he called Wooster Gardens. There he showed innovative photography and a number of women painters — among them Mary Heilmann, Ann Craven and Amy Sillman. In 1995, he gave Kara Walker’s provocative black paper silhouettes their first solo show.

Michael Jenkins began working with Mr. Sikkema in 1991, officially becoming a gallery director in 1996 and a partner in 2003. Meg Malloy became a partner in 2005.

Artists formerly represented by the gallery include Ms. Sillman, Mark Bradford, Wangechi Mutu, Deana Lawson and Arlene Shechet.

In 1999, Mr. Sikkema was in the early wave of gallerists moving from SoHo to far west Chelsea, which at the time was still a semi-deserted industrial neighborhood. There he showed glass sculptures by Josiah McElheny, photographs by Tim Davis and the mystical drawings of the Ivoirian outsider artist Frédéric Bruly Bouabré and, as Ken Johnson wrote in a 2000 New York Times review of a group show that included Barkley L. Hendricks and Wangechi Mutu, expanded his affinity for multiculturalism “not as a bureaucratic program but as a kind of delirious pluralism.”

Jeffrey Gibson, who this year will become the first Indigenous artist to represent the United States at the Venice Biennale, joined the gallery in 2018. He also shared a statement dwelling on Mr. Sikkema’s generosity.

“Brent was an early supporter of many queer art spaces including Participant Inc., FIAR and Boffo, among others,” he wrote. “He would always take the time to engage with artists, not like a dealer or gallerist, but more like a supportive friend.”