Although The Simpsons takes viewers to some interesting locations, many episodes focus on Bart and Lisa's experiences at Springfield Elementary School. Springfield Elementary has its fair share of bullies, but Nelson Muntz remains one of the school's most prominent and terrifying tormentors, but he hasn't always worked alone. Those that have been following The Simpsons from its early days may remember Nelson's sidekicks, the Weasels.
The Weasels are nearly identical apart from their skin color, which may be why writers chose to unusually name them Yellow and Black. Despite not having a starring role, the pair of bullies became familiar faces among fans; however, the Weasels were later demoted to background characters before disappearing entirely in The Simpsons' later seasons.
The Weasels primarily appeared in the early episodes of The Simpsons, flanking Nelson Muntz. However, after Bart defeated Nelson in Season 1, Episode 5, "Bart the General," the Weasels went from secondary characters to background regulars. Using military advice provided by Grandpa Simpson's friend, Herman, Bart recruits a small army of classmates, who attack Nelson with water balloons and capture him. The episode concludes with Bart and Nelson signing a peace treaty under Herman's supervision.
Although it's not entirely clear why the trio's friendship dissolved, it's likely the Weasels decided they'd be more capable bullies on their own after witnessing Nelson's defeat. From then on, Nelson essentially becomes a loner bully, occasionally teaming up with older kids Kearney Zzyzwicz and Jimbo Jones.
While the Weasels rarely join forces with Nelson again, the duo is frequently seen throughout the series in other bullying scenarios. The Weasels can also be spotted in background shots involving Springfield's children, establishing them as Lisa's classmates; however, they did not stay in her class for good.
Yellow and Black Weasel might not be the most famous of The Simpsons' characters, but the writers do provide insight into the boys' whereabouts after their disappearance. As revealed in Season 25, Episode 14, "The Winter of His Content," the Weasels transferred to Shelbyville Elementary. While the characters could return in a cameo, it's safe to say the mysterious bullies have since moved on to stealing lunch money in Shelbyville.