Who is "the stalker" in the novel, Yo!?

The stalker is the unnamed narrator of the chapter titled "The stalker." He has been following Yo for 25 years. They first met in a convenience store when he told her he had no money for food and she gave him a hot dog. He later showed up at her apartment in New Hampshire (where she lived above Marie Baudry), at which point she called the police and he was arrested. In this chapter, he holds Yo and one of her sisters at knife point in Yo's hotel room in Chicago while she is on her book tour. His strange, associative interior monologue makes it clear that he is mentally unwell, and he recalls disturbing events from his childhood that exacerbated his mental illness, like being beaten by his mother when he was five years old.