These are The Blockheads G and J from the Gumby cartoons. They're Gumby's archnemeses. They first appeared in "Little Lost Pony". They're criminals and troublemakers. They hate Gumby and his friends, but mostly Gumby, sometimes they even try to kill Gumby to finally get rid of him because he always ruined their plans and scams. G is the leader because he's the smarter, more aggressive and abusive of the Blockheads, while J is his sidekick who often slapped by G everytime he screwed up. They committed crimes like theft, fraud, swindling, counterfeit, murder, kidnapping, animal abuse, trespassing, vandalism littering, polluting and using illegal pesticides. Also, in the late 1980's episode, "Humbug", it revealed that The Blockheads hate Christmas because they were using a tank to destroy Christmas decorations and helping Ebenezer Scrooge to kidnapped Santa Claus.
Blockheads G and J are owned by DreamWorks Animation, Universal Studios and Premavision Inc.