Regarding intelligence. Liches are often former living wizards who voluntarily became undead, managing to separate their body and soul through forbidden rituals and kill themselves. In short, during their undead existence, they strive to improve their magical skills, but also hate the living.
I've heard about black knights – they are said to be cunning, good strategists, and skilled fighters. They are also undead with intelligence.

Regarding vampires – in Heroes of Might and Magic IV, they rule over the creatures. They are at their peak in that game.