Milne was one of the pirates who attacked the River Queen when Lief, Barda, Jasmine, and Dain were aboard. He captured Dain and retreated with the rest of the pirates when one of the passangers was revealed to be an Ol.
Milne knew that Dain was a member of the Resistance and planned to return him to Doom out of fear. The other pirates found out about this and decided to feed him to the Glus. By the time the companions were captured, he was broken and solemnly accepted his fate.
He was tossed into the Maze of the Beast with the companions, causing him to go into a panic. This attracted the attention of the Glus. It spun its webbing around his head and arm, causing him to run off blindly. The Glus followed after him, eventually capturing him and sucking the flesh from his bones.
Milne's role in the anime is the same as in the book. However, the pirates decide to feed him to the Glus because he tried to boss them around, rather than trying to return Dain to Doom. Also, he remained with the companions for a little after entering the Maze of the Beast, though he eventually broke and ran off on his own to be eaten. Lief was visibly upset at this.