Watson Brewer becomes the stepfather Kristy and her brothers when he marries their mother Elizabeth in book #6, Kristy's Big Day. He is also the father of Karen Brewer and Andrew Brewer and is divorced from their mother, Lisa Engle.
Elizabeth and Watson began dating about four months before Kristy began the seventh grade, and became engaged that October. They married at the end of June, two weeks after the end of the school year.
The precise reasons for Watson's earlier divorce are never explained. In #1, Kristy's Great Idea, he rushes to the hospital when his ex-wife breaks her leg, both to take care of insurance forms (Kristy supposes) and to help his ex-wife with her injury since her new husband is out of town. Kristy says that his divorce is "a friendly one." However, in the Baby-Sitters Little Sister series, the relationship between Watson and Lisa seems considerably more strained, although they are able to have discussions and work out arrangements regarding Karen and Andrew.
At the beginning of the series, Karen and Andrew spend every other weekend and some holidays with Watson. Later, they begin alternating months with Watson and their mother.
He is balding.
Watson owned Boo Boo since before he met his first wife.