Michal is one of David's wives and one of Saul's daughters. Although David had originally won her as his wife in 1 Samuel in exchange for "one hundred Philistine foreskins" (which he obtains by killing a hundred Philistines… we presume), she's since been remarried to a guy named Paltiel. But David wants her back—and gets her back, when Abner defects to his side.
Yet, despite this touching reunion, Michal plays a negative role when David brings the Ark into Jerusalem. Since David dances before God and the Ark in a somewhat scantily clad state (wearing but a linen ephod), Michal mocks him and says he should be ashamed for dancing in front of her maidservants that way. David says he's glad to abased in front of both God and her maidservants, and Michal is punished for her uptightness by never having any children for the rest of her life.