The following is based on Fallout Tactics and some details might contradict canon.
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That's far enough, ghoul licker! I can't let you ruin my plans. Those ghouls aren't human! Why would anyone want to give them regular, God-fearing, human rights? It ain't fair to all the honest pure bloods. My plan was perfect, and I would gotten away with it if it wasn't for you meddling soldiers.
The "Old Man" Withers, also known as the head assassin of ghoul-haters, was the leader of a raider group that came to Springfield in order to eradicate ghouls and overthrow the mayor Chris Avellone. He was in fact a young man skilled in combat, who used a shotgun against his enemies. The group he led, while appears to be just another raider gang, was in fact a party of ghoul-haters who were pissed off by the mayor's pro-ghoulish politics. The group was quite large and included not only regular members (called simply raiders in-game), but also some elite, experienced warriors called enforcers.