Who was the rat man in Harry Potter Deathly Hallows?

There isn't a specific character referred to as "the Rat Man" in Harry Potter and the Deathly Hallows.

It's possible you are thinking of:

* Peter Pettigrew (Wormtail): He was an animagus who could transform into a rat. He spent 12 years as Ron Weasley's pet rat, Scabbers.

* Scabbers: This was the name of Ron Weasley's pet rat, who was actually Peter Pettigrew in disguise.

Let me know if you meant one of these characters, or if you have another character in mind!