Richmond the Horse is a grey Muppet horse seen in The Muppet Christmas Carol. While his name wasn't mentioned in the film, Gonzo and Rizzo the Rat refer to him by name in the 20th anniversary audio commentary.
The character was devised by Dave Goelz, who performed the horses with David Rudman, as a tribute to the late Richard Hunt. Goelz named the character after Hunt and modified the puppet's teeth with a gap akin to one Hunt had for much of his life. Off-set, Goelz corresponded with director Brian Henson as Richmond, asking for more screentime.
The puppet is the same one originally used as Old Skyball Paint.