Actor Seymour Cassel arrives at Dennis Hopper’s birthday dinner in 2006. (Ethan Miller/Getty Images/CineVegas)

Seymour Cassel, an Oscar-nominated character actor who played raconteurs, street toughs and cha-cha-dancing hoodlums and who frequently collaborated with independent filmmakers John Cassavetes and Wes Anderson, died April 7 at a hospital in Los Angeles. He was 84.

The cause was complications from Alzheimer’s disease, said his son, Matthew Cassel.

Mr. Cassel had more than 200 film and television appearances, beginning with an uncredited role in Cassavetes’s 1958 directorial debut, “Shadows,” a largely improvised movie about three black siblings in New York.

He went on to become a film and television mainstay for five decades, taking roles that often reflected the prankish, street-wise reputation he had acquired off-camera, partying with the Beatles and the Rolling Stones. He also struggled with alcohol and drug use before sobering up in the 1980s.

Mr. Cassel was most closely associated with Cassavetes, an actor and pioneer of low-budget, deeply personal filmmaking whom he described as “the older brother I never had.”

“You could always add something to a scene because your instincts are to embellish it somewhat to contribute to the text,” Mr. Cassel told NPR’s “Fresh Air” host, Terry Gross, in 2006. “And ideas come to you and you try them. And if they’re good you keep them. If they’re not, you just eliminate them.”

Mr. Cassel in 2006. (Mark Mainz/Getty Images)

He served as an associate producer on “Shadows” and went on to appear in a half-dozen Cassavetes films, including “Faces” (1968), a study of loneliness for which he received an Oscar nomination for best supporting actor. He played a hippie, Chet, who spends the night with a lonely middle-aged married woman, revives her after she tries to overdose on sleeping pills, then leaps out her bedroom window and skitters down the roof after her husband comes home.

Three years later, he starred in the Cassavetes comedy “Minnie and Moskowitz,” as a moustached car-parker who woos a cynical museum worker played by Gena Rowlands, the director’s wife.

“Cassel is one of the few actors who can let everything inside hang out, because he’s got the stuff inside,” wrote Chicago Sun-Times reviewer Roger Ebert. “A lot of actors throw aside caution and reveal their innermost being, only to raise the curtain on a void. Cassel makes Moskowitz into a convincing, dedicated, pure crazy Romantic.”

Mr. Cassel went on to work with directors including Sam Peckinpah (“Convoy”), Elia Kazan (“The Last Tycoon”), Nicolas Roeg (“Track 29”), Warren Beatty (“Dick Tracy”) and Steve Buscemi (“Lonesome Jim”).

“In the Soup” (1992), in which Mr. Cassel played a wisecracking gangster to Buscemi’s straight-man, aspiring screenwriter, helped revive Mr. Cassel’s career.

“In making the film there were times I wanted to murder him — and I only say that because we’re so close,” the movie’s director, fellow Cassavetes disciple Alexandre Rockwell, told the Los Angeles Times. “It’s always a wrestling match with Seymour, and when he wants something he generally gets it because he’s extremely persuasive, relentless and totally unpredictable.”

Premiering at the Sundance Film Festival, the movie won the grand jury prize for best dramatic film and earned Mr. Cassel a special jury prize for acting. It also drew the attention of Anderson, who cast Mr. Cassel as the father of Jason Schwartzman’s eccentric teenage character in “Rushmore” (1998).

Mr. Cassel was later featured in two more Anderson films, as Gene Hackman’s pal and elevator-operator in “The Royal Tenenbaums” (2001) and as Esteban, a bald diver who is eaten by a shark in “The Life Aquatic With Steve Zissou” (2004).

In 2012, the Oldenburg International Film Festival, often described as the German equivalent of Sundance, named an acting award in his honor.

Seymour Joseph Cassel was born in Detroit on Jan. 22, 1935. His mother was a member of the Minsky burlesque group. Mr. Cassel, who never knew his father, joined her on tour as a young boy and soon began performing, pulling down the pants of clowns at matinees.

His mother married a master sergeant in the Army Air Forces, and the family moved to Panama, where his stepfather was said to have won a nightclub in a game of craps. After his mother filed for divorce in the late 1940s, she sent Mr. Cassel to live with his godmother in Detroit, where he soon joined a gang.

He later said that at 17, he was given a choice: Join the Navy, or go to jail. He picked the military, and after three years of service and a brief stint in college, he returned to Detroit, where he built props for a theater company and took small acting roles. Convinced he had a future in theater, he bought a bus ticket to New York, only to bomb at an Actors Studio audition.

His life, he told the Times, was “saved by John Cassavetes,” who was leading an acting workshop. Mr. Cassel was too late to join but asked whether he could watch the director film “Shadows.” He joined the film’s four-person crew, then followed Cassavetes to Los Angeles in 1959, living in the director’s guesthouse. Both men were ferocious drinkers, and Cassavetes died in 1989 of cirrhosis of the liver.

Mr. Cassel married Elizabeth Deering, who appeared alongside him in several Cassavetes films, in 1964. For a time, they lived next to the family of Saul Hudson, a young boy who later became the lead guitarist for Guns N’ Roses. Mr. Cassel was credited with giving him the nickname Slash, once explaining that it was because Saul kept running around his house, “slashing in and out.”

His marriage ended in divorce. Survivors include a daughter from an earlier relationship, two children with Deering, seven grandchildren, and three great-grandchildren.

Mr. Cassel was a board member of the Screen Actors Guild, which in 2009 suspended him for two years after an internal review board found that he had sexually harassed three female staff members.

In a hardscrabble life, the suspension was not the only incident that made news. He once got in an altercation with John P. Connolly, an actor and union leader. And in 1981, he served a six-month prison sentence for possessing and intending to distribute cocaine.

“Sometimes I’ll hear a piece of music that makes me feel nostalgic for the past and I’ll remember how simple times were and how sweet life used to be,” he told the Times in 1992. “But I can’t live in the past, because I’m fortunate enough to be able to say that this is the best period of my life. I’ve discovered there aren’t any scars that don’t heal and that you’ve gotta give up the scars, because if you don’t you waste your life. There’s nothing I can do about my past, and to regret it is indulgent.”