Just About Anyone

The Kingdom of Ugh is just like any other on the improbable planet of Morsus: full of unhappy humans and aloof magical creatures, and is ruled by a king who doesn't care much about anything beyond his next meal. So, for a brief moment of happiness, the subjects took matters into their own hands......and beheaded the king. Again. This is a problem for a wizard who can't perform spells properly and a witch who finds being a charlatan easier than magic.
They're ex's, and they took it upon themselves to provide a monarch to the kingdom as a bitter wager. Although, kingmaking is becoming more complicated than they anticipated, and now they must, yet again, try to find a ruler that can keep possession of something to put a crown on. But something has to change: regicide has become a matter of course for the subjects of Ugh. There is no tolerance left for the typical aristocrat, and the wager isn't over until one of them installs a successful king or queen.
Which one in this former fiery romantic partnership will be able to win the wager and, incidentally, make such unhappy humans happy at the same time?