He was the landlord of Popclaw. She accidentally crushed his head while he was giving her cunnilingus. The event was secretly recorded by the Boys who used it to blackmail Popclaw into revealing where she obtained her Compound V, with Billy Butcher threatening to upload Popclaw and Alesky on PornHub should she fail to cooperate.
After Popclaw's death A-Train re-watched footage of her with cameras he'd secretly installed without her knowing and saw her killing Alesky, much to A-Train's horror, which also led to A-Train learning about the Boys themselves.