Silla was born in a small village outside Rome, Italy. Silla trained as a circus performer, came to the United States in 1955, and toured with the Ringling Bros. and Barnum & Bailey Circus. His multiple talents as a bareback rider, trapeze artist and tumbler brought him to Hollywood, where he became a stuntman, starting with the Gig Young-Shirley Jones vehicle, A Ticklish Affair. His best-known roles are Litvak, the maniacal, miniature Hitler who menaces George Segal in The Black Bird (his favorite role), and Cousin Itt on the long-running TV series, The Addams Family. He was also responsible for the physical performance of the robot Twiki in the TV series Buck Rogers in the 25th Century, a role for which the voice was supplied by Mel Blanc or Bob Elyea. In part due to his short stature of 1.19 m (3 ft 11 in), he has often doubled for children in such movies as The Towering Inferno, The Hindenburg, and Battlestar Galactica. Between movies, he frequently appears in Las Vegas and Reno night clubs with his own musical combo, “The Original Harmonica Band”.
His audition for his most famous role, television’s “Cousin Itt” of The Addams Family, was as mysterious to him at the time as the popular character would soon be to millions of viewers. Arriving at the studio, he received little more than a quick looking over by the director and producer, who merely said “That’s Itt!” and told him to come back Monday morning and report for work. He returned home for the weekend, pleased to have passed the audition, but still completely unaware of who — or what — he had been hired to portray on The Addams Family. Not until Monday morning, just hours before he made his debut as “Cousin Itt”, did he have any idea as to the nature of the character.
He provided the voice of Mortimer Goth from The Sims 2, the best-selling video game of 2005. He also played one of the Ewoks in the movie Return of the Jedi.
Silla was almost killed while working as the stunt double for “Short Round” in Indiana Jones and the Temple of Doom during the filming of the river rapids scene. The life raft in which he was riding flipped over in the turbulent water and he was trapped underneath it for some time with a faulty inflatable life vest, nearly drowning until a safety diver could reach him and pull him to safety.