Shardik is one of the twelve guardians of the Beam that hold up the Dark Tower. It is a cyborg bear that stands over forty feet tall and has a contraption affixed to its head resembling a satellite dish (known as a thinking cap by Roland). King probably named him after a 1974 fantasy novel about a hunter who pursues a giant bear he presumes to have the power of God.
The bear at the end that Trisha faces is the bear known as Shardik from the Dark Tower. Throughout the entire story, Trish follows a stream, the way of the land, and a road. It's said that everything follows the beams, and Trisha followed the bear beam by following the land while she was lost. When she encounters the bear, it is covered with bugs and maggots just like Shardik. She pretends to throw a pitch at the bear, which results in "batteries" falling out of him (which hints that the bear is robotic just like Shardik).
Grown men would have turned and run from the Ursus americanus which lumbered out of the last screen of bushes - it was a fully grown North American black bear, perhaps four hundred pounds-but Trisha had been prepared for some awful horror torn from the underside of the night.
- Bottom of the Ninth: Save Situation