Caligula - Jay Robinson
Excellent performance - but then he stumbled:
From IMDB:
"After his movie bow, Jay went on to reprise the "Caligula" character in Demetrius and the Gladiators (1954) with Mature and Susan Hayward, and offered typically eye-catching supporting turns in The Virgin Queen (1955) starring Bette Davis, and My Man Godfrey (1957) with David Niven and June Allyson.
It was at this juncture, however, that things started going horribly wrong for Jay. His newly found celebrity went to his head and made him extremely difficult to work with. In addition, the volatile actor began experimenting recklessly with drugs. In 1958 he was booked for possession of narcotics (methadone) and sentenced to a year in jail. Freed on bail, the incident and resulting notoriety ruined his career.
After scraping up work outside the entertainment industry as a cook and landlord, he recovered from his drug addiction and married. Resuming work in obscure bit parts, he had another career relapse when he was forced to spend 15 months in jail after an old warrant was served on him."