Curse of the Crimson Throne
The Crimson Throne is the throne of the ruler of Korvosa. The throne, and thus the monarchy itself, is said to be cursed, and each ruling king or queen of Korvosa has died without a direct heir as a result.
Additionally, no monarch has yet died of natural causes. Every ruler has perished at the hands of another, either through subtle or overt methods.
The current ruler on the Crimson Throne is King Eodred II.