Supposedly Bloch asked Lovecraft if he could use him in a story. Lovecraft replied that Bloch could “portray, murder, annihilate, disintegrate, transfigure, metamorphose, or otherwise manhandle” him in a story. Bloch wrote The Shambler from the Stars where he killed the Lovecraft like character. He even dedicated the story to Lovecraft.
Lovecraft answered with The Haunter of the Dark with a Robert Bloch character named Robert Blake who he of course kills. He even went so far as to use Bloch's current address as Blake's in the story. Lovecraft dedicated the story to Bloch.