Who is Thomas Lyon from The Winthrop Woman and what is their importance?

Thomas Lyon is Joan's husband. He is described as a lazy man, who hopes to cash in on the fact that he has married a Winthrop. Thomas tries to take over as head of her household when he marries Joan, and he even managed to coerce the mentally ill Robert into retracting his grant of the property to Bess and Will Hallet. He is an opportunist, whose treachery serves to estrange Bess from her daughter until her daughter's death.