Born: c. 1495, Died: c. 1526
Known for: Being "Gentleman of the Privy," which has nothing to do with the toilet. (Source)
William Carey is Mary's first husband. Normally, husbands aren't too happy when their wives sleep with other men. But William isn't a normal husband. He doesn't love Mary, anyway; plus, he profits from Mary's infidelity, so he doesn't care to stop it. The longer Mary is off seducing Henry, the more land and wealth comes William's way.
When William realizes Mary won't be queen, and that he can no longer profit, he decides to act like her husband, after all. "You are going to face the enmity of Queen Katherine herself, and the hatred of all of Spain. I shall spare you mine" (9.98). At least he's nice about it, we guess?
Mary works to reignite the passion with her husband, but it's difficult to reignite something that was never ignited in the first place. Like all marriages at this time, this marriage was arranged by Mary's family as an order of business. William is sweet at times, and he puts effort into courting Mary, but he does so for ultimately selfish reasons. Like Henry VIII, William only wants a male heir.
He dies before that happens, and Mary is kind of thrilled about it. "His death had set me free. If I could escape another husband, I might buy a little manor farm on my family's lands in Kent or Essex" (21.71). Mary realizes she doesn't want another husband—but another William, who is totally different from this William, later changes her mind.