"He was a gentle man, but he was also a gentleman. He treated people with respect and dignity."
Ostrum, now 58, was chosen at the age of 12 from a pool of thousands of young hopefuls hoping to land the part of Charlie Bucket in the adaptation of Roald Dahl's children's book.
Willy Wonka is Ostrum's only film credit. He is now a veterinarian in northern New York.
"Gene's wit and humour spoke to many generations of film audiences," Ostrum commented to ABC News. "He was a unique talent that brought joy to all of us that followed his long career."
"As a young actor filming Willy Wonka, I had the rare privilege of working with Gene who I greatly admired," he said. "He became my mentor and personal friend. For that I will always be grateful. So shines a good deed in a weary world."
Wilder passed away on Sunday at the age of 83 of complications from Alzheimer's disease. Many of his other Willy Wonka co-stars have paid tribute to the late actor.