The Bear

The Bear, originally called Shardik, but named Mir (meaning "the world beneath the world") by the Old People, was a guardian of the of the portals of the beam. It sits at the opposite portal to the Turtle.

A "cyborg" of the bear was created by a company called North Central Positronics Ltd, in Granite City, Northeast Corridor.  It was a Design 4 Guardian, part flesh, part robot, with the serial number AA 24123 CX 755431297 L 14. It was designed to protect the portal.

It had been around for perhaps thousands of years, but when Roland and his group encountered the Bear, it was dying, having gone crazy over the centuries, and was full of white parasites.  It was killed by Susannah Dean shooting it in the radar disk ("hat") on it's head.