Wendy Haverford is Tom Haverford's ex-wife. She is a successful surgeon with a pediatric surgery fellowship.
It is learned in the second season by Ron Swanson that Wendy and Tom's marriage is a green-card marriage, and that she is from Canada.
Ron and Wendy begin a relationship in Season 3, which troubles her ex-husband Tom so much that his girlfriend Lucy breaks up with him. In "Ron & Tammy: Part 2", Ron's ex-wife Tammy 2 continues her efforts to sabotage his life, but the normally susceptible Ron easily resists her seductions because he is now in a solid relationship with Wendy.
Later, however, Wendy and Ron break up after she announces she is moving back to Canada to be closer to her parents. She asks if Ron would want to move up there with her, and he laughs at the idea.