John Chanler was a fellow Monstrumologist who suffered the delusion that he was a Wendigo and died in the Curse of the Wendigo. He was also Pellinore Warthrop's best friend.
Went to Boarding School with Pellinore and often played practical jokes on him when they were young.
Apprenticed with Pellinore under Von Helrung in New York.
Curse of the Wendigo
Before the series John was a handsome hardy man who was far healthier than his friend Dr. Warthrop. But after he goes missing he losses his sanity and becomes very bony and skinny (due to him starving while being held captive). By the end of the book. He his unkept and refuses to eat anything but human flesh. His breath smells of rotting flesh, and his sanity is completely gone.
Not much is known about their relationship since by the time the book starts John's sanity has already left. What we do know, is that Muriel and John are husband and wife, as they met over Pellinore's sick bed after he jumped off the Kronprinz-Rudolph Bridge. It can be assumed that he loved her and trusted her very deeply. Although he ends up killing her in the second book, this can be explained by the fact that he had completly lost his mind, and probably didn't recognize her.
John Chanler and Dr. Warthrop had a strong friendship which was damaged when John fell in love with Muriel and they got married. Although their friendship was damaged it is clear they still cared for each.