Gus Solomons Jr., who as a dancer, choreographer, educator and critic was a leading figure in modern and postmodern dance, died on Aug. 11 in Manhattan. He was 84.

His death, at Mount Sinai Morningside Hospital, was confirmed by Robert Gerber, Mr. Solomons’s friend and health proxy, who said the cause was sudden heart failure after several months of declining health.

Over his long career, Mr. Solomons danced with many companies and many choreographers, including Martha Graham and Merce Cunningham. He broke ground as the first Black dancer to join the Cunningham company. (There were only four in the company’s history, all of them men.)

In an interview as part of the YouTube series “Mondays With Merce,” Mr. Solomons said that he loved taking Cunningham’s classes, but that he “never aspired to be in the company because I didn’t look like anybody in that company.”

He was referring not only to his race but also to his height: A picture of lanky elegance with incredibly long legs, he was 6 feet 3 inches tall. One night, Cunningham invited him to dinner. “We had Italian food, and he said, ‘I think I’d like you to dance with us,’” Mr. Solomons recalled. “And it was like a movie. I mean I just sort of floated home.”

While a member of the company, from 1965 to 1968, Mr. Solomons originated roles in several important Cunningham works, including “Variations V,” “How to Pass, Kick, Fall and Run,” “Scramble” “RainForest” and “Walkaround Time.”

He left after three years when a back injury impeded his ability to jump. With rest, he healed, and a few months later he was back to dancing and also focusing seriously on choreography, notably the dual-screen video-dance “City/Motion/Space/Game,” which he created for the Boston public television station WGBH. In 1972, he formed his own group, the Solomons Company/Dance.

Mr. Solomons never stopped experimenting in the decades to follow. Douglas Nielsen, a member of his company from 1973 to 1975 and a longtime friend, called him “a major trunk to our dance family tree.”

Mr. Nielsen compared Mr. Solomons’s choreography to a crossword puzzle of steps. “He drew stick-figure drawings on graph paper for us to decipher, never knowing if there would be a sound score,” he said in an interview. “One time at Larry Richardson’s Dance Gallery, he played Jimi Hendrix super loud as the audience entered, and then shut it off as we proceeded to dance in silence for an hour.”

The dancers in that performance were as surprised as the audience. “Like John Cage says, there’s no such thing as silence,” Mr. Nielsen said. “And that was profound.”

Gustave Martinez Solomons Jr. was born on Aug. 27, 1938, in Cambridge, Mass., one of two sons of Gustave Martinez Solomons, an engineer, and Olivia Mae Stead Solomons, a teacher.

He started dancing when he was 4, but he didn’t begin training until he was a freshman at the Massachusetts Institute of Technology, where he earned a degree in architecture. All the while, as he wrote in the 2003 book “Reinventing Dance in the 1960s” (a collection of essays and interviews edited by Sally Banes with the assistance of Andrea Harris), he had “a burning itch to perform and make dances.”

He moved to New York in 1961 to dance in “Kicks & Co.,” a Broadway-bound show with choreography by Donald McKayle, but it closed after four previews in Chicago. Once in New York he continued his training, studying modern dance on scholarship at the Martha Graham School and ballet at the Joffrey Ballet School. He danced with Joyce Trisler and Pearl Lang, among others, and was part of the original group that went on to form the Judson Dance Theater collective, but in the end went his own way.

Mr. Solomons relished technique, both in his dances and in his own dancing. As he wrote in Dance Magazine last year, “I was not willing to ditch technical dancing after working so hard to gain some measure of proficiency at it.”

A prolific choreographer, he created more than 150 dances for his group. “My dances experimented with game rules to create accidental juxtapositions and unpredictable images,” he wrote in “Reinventing Dance.”

The choreographer Donald Byrd said that dancing in Mr. Solomons’s company, which he joined in 1972, was a great experience.

“There’s a joke about Gus,” he said in an interview, laughing. “Gus was really mean then. And so one of the things we said later is, ‘When did Gus get so nice?’ Because there was a point somewhere in the ’90s that he was kind of transformed into this really nice, likable person that everybody loved and wanted to be around.”

Mr. Nielsen denied that Mr. Solomons was ever mean; it was simply, he said, that “he knew what he wanted.” And his approach, Mr. Byrd said, didn’t feel personal: “He was doing it to contribute to you, to wake you up, to make you more conscious, more aware of what you were doing. And so I loved that about him.”

Mr. Solomons went on to dance the role of the father in Mr. Byrd’s “The Harlem Nutcracker” (1996), which made sense: To Mr. Byrd, he was something of a father figure in his life. “He was,” Mr. Byrd said, “the perfect dancer to work with.”

In 1996, Mr. Solomons joined forces with Carmen de Lavallade and Dudley Williams to create the performance ensemble Paradigm, which showcased mature dance artists. “We were quite a trio,” Ms. de Lavallade said in an interview. “Gus was terribly imaginative. He was just a cool guy. We had a lot of fun together.”

A radiant and elegant force in the dance world, Mr. Solomons was also an educator — he was a professor in the dance department of New York University’s Tisch School of the Arts from 1994 to 2013 — and a dance critic for publications including The Village Voice, Ballet News and Dance Magazine.

But beyond his dances and his writing, Mr. Solomons, as a Black man in downtown experimental dance, was a rarity. “Gus’s presence in that white space of New York experimental dance was really important,” Mr. Byrd said. “And it made it all right for me to want to explore that way as a choreographer. And I think that was probably true for other people as well.”

Information on Mr. Solomons’s survivors was not immediately available.

Mr. Solomons’s archives are housed at the Jerome Robbins Dance Division at the New York Public Library for the Performing Arts.

Throughout his life, no matter the state of his body, Mr. Solomons never stopped moving. When he was 79, an article in The New York Times about aging dancers quoted him as saying, “The reason I’ve been able to dance for so long is absolute will power.”

People responded to his performances in his later years, he said, because “I am playing the instrument as hard as it can be played, given the instrument.

“Yes,” he added, “my body is my friend, my body is my enemy.”