Lars Ulrich was the principle artist in the case of Napster versus RIAA in addition to being the drummer for Metallica. He complained that when kids used "Napster" they were stealing money from him. He has been made ridiculed numerous times because of his accusations.
During the court case, and even after, Ulrich is still seen as the poster boy for destroying Napster, and trying to destroy the idea of sharing music on the internet. Even if he was only being used by the company, his name has become almost synomous with the case.
The fact that he made millions already has hurt him, as well as many people accusing him that Metallica's popularity grew from swapping and copying tapes of the band, which is the same idea behind Napster and other music-swapping programs.