Slayer

Slayer is a title.

First War
In Warcraft: Orcs & Humans, it is a rank you can achieve, slightly under the one of Warchief.

Second War
In Warcraft II: Beyond the Dark Portal, it is the title held by the player character in the Horde of Draenor campaign. As Slayer to the Shadowmoon clan, the character has the duty of leading their armies into battle and as such the rank seems similar to the one described in the previous game.

World of Warcraft
Upon completion of the demon hunter class hall quest campaign, the player shall be granted the title of Slayer.