He was indignant about being nominated, due to the "dirty back room politics" of the Justice Bloc. He is referring to the fact that the Justice Bloc leaders had forced his wife, Katherine to perform sexual favors for them or they would nominate Nathan for Overseer. They did so after that regardless, and Katherine began murdering Justice Bloc members to ensure her election as Overseer. This led to the "I hate Nate" posters being changed to "I hate Kate."
Nathan Stone is mentioned only in Fallout: New Vegas.