Henriksen's first film appearance was in It Ain't Easy in 1972. Soon afterward, he graduated from the Actors Studio and began acting in New York City. For his first role, he put the entire script to tape with the help of a friend, learning everyone's part in addition to his own. Illiterate until then, it was around this time that he taught himself to read.

His first theater work, around age 30, was as set designer, and he received his first acting role because he built the set for a production. Henriksen found work as a muralist and as a laborer on ships. JSTOR ( August 2017) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.

He served in the United States Navy from 1955 to 1958 and attained the rank of petty officer third class. He left school after completing first grade, and was illiterate until the age of 30. Growing up, Henriksen had a reputation for getting into trouble in the various schools he attended, and even spent time in a children's home. On another occasion, two of his uncles tried to persuade him to take Methadrine and then take part in a staged car accident for the insurance money. I'm not having a pity party here I'm not Quasimodo. I remember every single face from my childhood. Henriksen did not actually leave home until he was 12, saying he'd 'had enough' of his home life, and that he had been physically assaulted by multiple family members: 'I got bludgeoned a lot. During an interview, Henriksen recounted how, at the age of seven, his mother handed him his birth certificate, said, 'You'll always know who you are', then pushed him out of his home.

His parents divorced when he was two years old, and his mother struggled to raise him and his brother, leading to his spending part of his childhood in foster care. His father, James Henriksen, was a Norwegian merchant sailor and boxer nicknamed 'Icewater' who spent most of his life at sea, while his mother, Margueritte Werner, struggled to find work as a dance instructor, waitress and model. Henriksen was born on May 5, 1940, in Manhattan, New York.

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