What was Syndrome's real name before becoming a villain?

Syndrome’s real name was Buddy Pine.

Before becoming Syndrome, Buddy Pine was a highly intelligent child who called himself Mr. Incredible’s “number one fan.” He had no superpowers, but he invented gadgets and dreamed of becoming Bob Parr’s sidekick under the name IncrediBoy. Bob rejects the idea, insisting that he does not need a sidekick.

During an attempted confrontation with the villain Bomb Voyage, Buddy interferes and nearly causes a disaster. Bob rescues him but turns him over to the police, leaving Buddy humiliated and embittered. That rejection becomes the foundation of his later vendetta against Bob and other superheroes.

As an adult, Buddy reinvents himself as Syndrome, a wealthy weapons inventor. He develops advanced technology, including the Omnidroid, and uses it to eliminate superheroes while pursuing artificial hero status for himself. His real identity is sometimes confused with other civilian names in the film: Robert Parr is Mr. Incredible, Lucius Best is Frozone, and Bob’s children include Dash and Violet Parr.