The Clowns are a rival bike gang of the Capsules in Neo-Tokyo, led by Joker. They are very violent, and are involved with the production and consumption of drugs.
The Clowns ambush Tetsuo when he's separated from the rest of the Capsules until they are fought off when Kaneda arrives on the scene to intervene.
Tetsuo crushes the head of a member of the Clowns, intimidating them into them into letting him become their leader, and to gain a supply of drugs to keep the migranes caused by his powers in check. The Clowns are disbanded after they are attacked by a union of the remaining biker gangs in Neo-Tokyo, led by Kaneda, and the Capsules. Tetsuo is taken by the military, and the Clowns are disbanded after their final battle against the Capsules.