Thor is a Norse god's name, very rarely (AFAIK) used as a given name; yet - Mrs. Callum's daughter and Robert Mitchum's love interest in Pursued (1947) is named "Thor". Why is that?
The actual character name is Thorley, not Thor.
This character is called as Thor and Thorley. Therefore, it can be assumed that this character is named Thorley and has been called Thor as nickname throughout the movie.
From the script,
I've come because of what you did to Thorley.
Go on home, Prentice. I don't want to hurt you.
Defend yourself, Mr. Rand.
I wouldn't try that if I were you, Grant.
Let's get him in the office.
I did it for Thorley.
Across the various online sources, this character has been listed as Thor (short for Thorley).