For starters, Mr. Lockton is a staunch loyalist and slave owner. Being a loyalist, he is loyal to the British empire and at various points throughout the novel attempts to bribe various patriots and plots to assassinate George Washington. Not only is he an evil presence in the overarching, patriotic sense of the word, but he is a violent and cruel man. While not all slave owners were physically abusive, they still contributed to the enslavement of black people, and Mr. Lockton is certainly physically abusive—frequently beating not only slaves Isabel and her epileptic daughter Ruth but also his own wife and family members.
Elihu Lockton's spousal abuse extends beyond regular physical abuse. He conceals the evidence of his sedition in his wife's dresser, which, if found, would cast suspicion on her, and it is likely he would betray her if that were to happen.