Jack-Jack Parr

Jack-Jack Parr is one of the main protagonists in The Incredibles.

The Incredibles
Jack-Jack is the youngest child in the Parr family; his parents are Mr. Incredible (Bob Parr) and Elastigirl (Helen Parr). His primary power is shapeshifting, but has a large number of other powers.

For the first few years of his life, Jack-Jack didn't seem to exhibit any signs of powers, presumably being too immature for superpowers to manifest.

When the rest of his family was occupied with Syndrome, Jack-Jack was looked after by Kari McKeen. But her determination to have some fun ended with trouble when Jack-Jack began showing signs of his powers which she tries to control and eventually anticipates. Later, Syndrome shows up, claiming he's the replacement baby sitter. When Syndrome attempts to openly kidnap Jack-Jack and fly away, Jack-Jack uses his powers to defend himself against Syndrome, ultimately resulting in a chain reaction of events that would lead to Syndrome's demise.

Edna Mode made costumes for the entire family, including a flame-retardant jumper for Jack-Jack which, ironically enough, is needed as Jack-Jack has the ability to burst into flames, though this being done before the family could determine the full extent of Jack-Jack's powers. Edna will presumably modify the costume to accommodate all of Jack-Jack's abilities.

Jack-Jack Attack
In the DVD short, Jack-Jack is now the titular protagonist.

Rick Dicker interrogates Kari, who has been having trouble trying to control Jack-Jack.

Later on, she says she wishes she could just forget the whole thing, and Dicker reassures her that she will, and uses a device to erase her memory.