Yokochini, also known as Weasel in the English dubbed anime, is a student of a different Karakura Town high school than that of Ichigo Kurosaki. He is the leader of local a gang of thugs.

Yokochini is a stereotypical juvenile gang leader. He mostly steers clear of violence, allowing his cronies to do the dirty work for him, counting on their obedience and fear of him to keep them in line; although he could never stop them from calling him Yokochini, a name he dislikes. Whenever his victims fail to quake with fear in his presence - or in Chad's case, refuse to fight back - Yokochini typically becomes unnerved. He can prove quite devious when he puts his mind to it, like having his goons attack Chad only to run away when Ichigo arrives, leaving an open line to him so he can spy on their conversation and find out the best way to hurt Chad. When the violence does reach him, however, Yokochini falls down as fast as the next man.

(Source: Bleach Wiki)