Credit: Everett Collection

Jeff Conaway, whose career on screens both big and small spanned from playing the wisecracking rebel Kenickie in the iconic 1978 movie musical Grease to sharing his heartbreaking descent into addiction on two seasons of VH1’s Celebrity Rehab, died Friday at the age of 60, his manager tweeted. He passed away from complications from pneumonia.

Born in New York City, Conaway shot to fame in the ’70s as a quintessential cocky guy: first in the internationally successful Grease and then on the TV hit Taxi, on which he played a similarly brash struggling actor named Bobby Wheeler from 1978 to 1981 (he left the show for its last two seasons). In 1980, he married Grease co-star Olivia Newton-John’s sister, Rona, and had a son named Emerson, though the couple divorced five years later.

After Taxi, his career never quite recovered. He snagged roles on The Bold and the Beautiful in 1989 and Babylon 5 in the ’90s, but his most disturbingly memorable appearance came when he appeared on Celebrity Rehab as one of Dr. Drew Pinsky’s most difficult cases. After a long struggle with addiction, he first appeared on the show’s 2008 season to fight a dependency on alcohol, cocaine, and painkillers. His mumbling, drunk arrival at the Pasadena Recovery Center in a wheelchair, as well as his airing of suicidal thoughts, caused alarm even in the most jaded viewers.

The actor had said in more recent public appearances that he was doing better, but on May 19, he was admitted to a Los Angeles hospital after being found unconscious in his Encino, Calif., home. He remained in a coma for two weeks.