Complex sentence: However, he is perhaps best known as the creative force behind the loosely autobiographical film "Withnail and I" (1987) which he based his time as a struggling out-of-work actor.
Split into simpler sentences: However, he is perhaps best known as the creative force behind the film "Withnail and I" (1987). Loosely autobiographical, he based the film on his time as a struggling out-of-work actor.