Rocko the Clown is a villain from The Powerpuff Girls comic book, "Rogue Clowns". He is a child's birthday clown, who went mad and started attacking everybody.
In "Rogue Clowns", the kids of Townsville were all having fun, celebrating at Scotty's birthday party. Scotty's parents invited in Rocko the Clown as entertainment. All of the kids had fun with him except for Bubbles, who was afraid of him. Kids all told Rocko to do things like make balloon animals, give them piggyback rides, do funny dances, and do other random things for them.
Rocko was having a bit of a difficult time, juggling all of their orders and things only started to get worse for him, when kids started throwing eggs and pies at him and insulting him for no reason. Rocko's rage started to boil up inside of him and he was just barely restraining himself from beating all the kids to death, but he still managed to scantily cling on to his happy facade. Just then, Bubbles conquered her fear of the clown and walked up to him and politely asked him to make her a unicorn balloon. This was the final breaking point of Rocko, as it caused him to finally snap and start lashing out at all the kids. Rocko screamed and yelled at the children telling them that they were all so demanding and abusive and that he was sick of dealing with all of their crap. The kids were reasonably frightened and Scotty's parents came in to scold him for acting so unprofessional and non-kid-friendly. Rocko took out his seltzer bottle and squirted the parents with a blast of water so strong, that it knocked them out cold. Rocko laughed maniacally and escaped the building, leaving Scotty's parents unconscious and the kids at the party traumatized for life.
The Powerpuff Girls flew out to stop him and chased him into an alley, where they found him leading a group of other evil clowns, planning a huge attack. Rocko narrated how he used to be a prisoner, who had to do community service as a birthday clown just to get out of jail. This story was the case for all the other clowns. Rocko said that now they were going to start an uprising and attack all of the kids in Townsville with a bunch of stupid clown toys like laser seltzers, exploding pies, and rabid balloon animals.
Rocko and his clown posse wreaked havoc on the city and The Powerpuff Girls started beating them up by using their own weapons against them. However, the clowns were still too powerful for them and they needed some backup. So, they went back to the party and got Scotty and all of the kids at his birthday party to come together and form an army so that they could all get revenge on the insane clown posse and defeat them. The kids all swarmed the clowns and beat them silly and eventually won the war. The police came to arrest them and take them to jail, where they would be rehabilitated again, this time into circus clowns. Bubbles noted how it was a horrible idea to keep allowing these repeat offenders to go back into society again, knowing that if they became circus clowns, they would only start causing these crimes again. Blossom and Buttercup assumed that the only reason she was saying that was because she was still slightly afraid of clowns and that these rational fears were completely unreasonable. They told her that there was nothing to worry about and flew off with her, allowing for the impending return of the rogue clowns to inevitably happen as soon as they got out of jail.