Jack's parents, Bennett Kilburn Mercer and Nola Margaret Miller, who professionally went by the stage name Nola St. Claire, were both actors, yet Jack diverged from the family path to pursue his true passion for art.
In his early days, Jack landed a position as an inbetweener, which is to say a rookie animator, at the renowned Fleischer studio. It was during his time at the studio that a serendipitous event took place, as Jack was singing the iconic Popeye theme song in a humorous tone, which caught the attention of none other than Dave Fleischer himself.
Impressed by Jack's vocal talents, Dave Fleischer extended an invitation to Jack to try his hand at voicing a cartoon. This initial foray into voice acting ultimately led to Jack being promoted to the role of writer at the Fleischer studio, where he continued to hone his craft and make a name for himself in the world of animation.
