Ralph Drinkwater crosses paths with Dominick Birdsey often. They went to school together, worked together during a summer break from college, and Ralph is the janitor at Hatch, the institute where Thomas is kept.
He shares a few parallels with Dominick. Ralph is also a twin, but his sister Penny Ann was murdered and dumped over the falls while they were in grade school. And although Dominick thinks that the universe is out to get him, Ralph is Native American, so he actually has a valid reason to be angry about being oppressed—not only were his ancestors slaughtered and driven out of town, but he continues to experience prejudice, like when his history teacher ridicules his entire race in front of the class.
Because Dominick doesn't have enough problems of his own, he also wallows about unfairly Ralph Drinkwater is treated, even when Dominick himself is treating him unfairly, like when he lies to the police and tells them that Ralph has large quantities of pot with intent to sell.
It's worth noting that Dominick (and Lamb) uses Ralph as some sort of symbol for Native American oppression, and Dominick's white guilt about it, but in doing so, Ralph and his race continue to be objectified for the white man's benefit.
We never really learn anything about Ralph. His sister died, he was sexually abused by a man who took him in, and he becomes a janitor. He tries to help Dominick by giving him news about Thomas, but Dominick never asks Ralph about himself.
Thing is, it turns out that Ralph and Dominick are cousins—Dominick's birth father is Ralph's uncle. And this is how Dominick magically absolves himself of his white guilt: by becoming Native American himself. When the Wequonnoc tribe opens up the Wequonnoc Moon casino, Dominick cashes in, right alongside the rest of them.
Ralph knows all along that Dominick is his cousin, and for much of the book, he thinks Dominick knows, too, and is just a total jerk. After all, Thomas knows, because Ma told him, and this is why Ralph looks after him—he's family.
When Dominick finally finds out, Ralph tells him, "Wequonnocs pray to roundness. […] Wholeness. […] The roundness of things" (47.232). We're not sure exactly what he means by that, but it seems to be something about how people eventually find completeness and closure, which Dominick does, whether or not you think he does anything to deserve it.