Final answer:
Orson Welles' last movie role was as the voice of Unicron in 'Transformers: The Movie', released in 1986.
Step-by-step explanation:
The legendary Orson Welles' last movie role was the voice of Unicron in C. Transformers: The Movie. This animated film was released in 1986, which was after Welles had passed away. Orson Welles was an iconic actor, director, writer, and producer, gaining fame for his innovative work in radio, theatre, and film. His final role in Transformers: The Movie showcased his remarkable voice acting skills, though it was a departure from the kinds of roles he was traditionally known for. Welles' contribution to cinema remains highly influential, and he is often remembered for his classic film Citizen Kane, which is frequently cited as one of the greatest films ever made.