Character Analysis
Ah, Dwight. What can one say about an insecure, obsessive compulsive, verbally abuse, drunk, borderline sociopath? Well, if you're Jack's mom, you say "I do," and rob your only son of any shot at a happy childhood. That's the central dilemma that Jack faces in the book.
Two Faced
Dwight starts out "very nice, very considerate." (7.21) until he gets Jack's mom to marry him. Then he transforms into a complete monster… not only with Jack, but eventually with mom too:
He pulled his hunting knife out from under the seat and held it to her throat. He kept her there for hours like that, making her beg for her life, making her promise she would never leave him. (22.56)
So yeah. Scary. Not only because he changes his tune so dramatically once they're married, but also because he puts on faces to get what he wants. Kind of like Jack himself, or in this case, some kind of demented evil twin version of Jack. Both he and Dwight adopt personas that hide the real person inside. Only in Jack's case, he's just a kid and is still figuring out who he is. Dwight knows who he is and hides it in order to get people close to him. Seriously, that's evil.
Compensating for Something?
We're not sure what Dwight's motives are—Wolff doesn't speak definitively about them and he may not care—but he seems to be trying to form some kind of perfect family. That involves a lot of smothering over-attention with a thick helping of criticism:
As soon as we got home, Dwight sat down at the kitchen table with a glass of Old Crow and reviewed my performance. (11.23)
The booze suggests that Dwight is a drinker—and seriously, who the heck slams back a glass of Scotch while talking to their kid?—and also that his criticism isn't entirely under control, since he's drunk while he does it. We get a vague unease with the line that ties in very neatly to Dwight's over-criticism.
He keeps trying to "improve" Jack by making a man out of him. He exercises authority without any of the responsibility—your garden variety power trip that would leave scars even if he didn't beat on Jack. That ultimately leaves him something to be avoided or escaped: an all-around bad guy who doesn't leave Jack particularly interested in why he's such a jerk.