I want to know if anyone knows of any Kings or Queens who were serial killers, not exactly mass murderers?

Thank in advance.

Royalty rarely did their own killing, so if you want the ones who got others to do it for them, the list would take all day to write.

Read up on the Borgias. Queen Ranavalona I of Madagascar against Christians. Caligula and Nero. Catherine de' Medici and the St. Bartholomew's Day massacre of the Hugenots.

Poor Lucrezia, beautiful but illegitimate daughter of a pope, 5 husbands by the time she died at 49, has endured centuries of bad reputation, and is now being seen as more of a pawn.

All royalty with the power of High Justice can be viewed as serial killers, if you don't believe in the Death Penalty. Likewise all warrior/conqueror kings could be considered serial killers. Judging historical figures by today's standards is tricky.