King Lathas is one of the main antagonists of Runescape's Plague City storyline, which takes place primarily in Ardougne. He is not considered overly popular among his citizens, as he is willing to look the other way if criminals successfully manage to bribe him.
At first, it appears that he is initially trying to protect the west side of Ardougne from a plague, and that his evil brother King Tyras is an enemy to Ardougne. Eventually, he persuades the player to murder his brother after they assist him in killing Iban, a crazed Zamorakian who was preventing him from reaching the land of the elves.
However, it is eventually revealed that King Tyras (thought to be a tyrant) was in fact an ally of the elves and that he is actually a sociopath trying to reawaken the Dark Lord so that he could destroy Camelot. The plague surrounding West Ardougne had in fact been conceived by him so that he could gather slaves to mine to the Temple Of Light, with the infected slaves being taken by the Mourners for this task.
In retaliation, the player seals off the Temple Of Light to prevent he and the mourners from activating the Dark Lord.
Eventually, his comrade Lord Iorwerth decides to sacrifice the remaining citzens of West Ardougne to the Dark Lord so that they could release it from its prison. King Lathas agrees to the plan, hoping that he could turn West Ardougne into his personal garden once it was depopulated.
However, the player character eventually rallies East Ardougne against him, as well as Tyras's vengeful guards. Regardless of whether the player character chooses to spare his life, he will still die.
Along with Sigmund, he is only of the only human characters in Runescape to be considered purely evil, with both of them willing to commit genocide.