Blockheads

The Blockheads are a group of mischievous hooligans with toy blocks for heads who act as the main antagonists of Gumby. The most recurring of the Blockheads are G and J who are considered Gumby's arch enemies. They bring pranks, mischief and chaos wherever they go, always finding ways of ruining everyone's fun and causing as much havoc and misfortune as possible, however their simplistic nature keeps them from doing anything too serious, nonetheless they are still capable of many nasty and cruel deeds and always have plans to make everyone as annoyed and miserable as possible. While they tend to mess up at times, they can be quite cunning and while they are usually defeated, they still manage to find ways to ruin everyone's fun for a good amount of time. J and G also have a special dislike for Gumby and go to many lengths to ruin his fun, such as stealing from him, pranking him and even attempt to kill him on a few occasions through either elaborate means or just by trying to crush him with a giant book.

Defeats

 * Defeated every time, but still manage to get away with some mischief

Appearances in Other Media
The Blockheads made an appearance in the stop-motion series Robot Chicken, where they were on trial for the murder of Gumby. J apparently brutally killed Gumby after he lost patience with him after Gumby spat in his face. J was quite proud of his deed while G feared getting the Death Penalty. In the end both received the Death Penalty and were ground up into clay and buried.