Juggernaut
Not to be confused with the X-Men villain, bitch.
A Juggernaut of Khorne is a daemonic steed. It is shaped roughly like a cross between a dog, a rhino, and a bull. The Juggernaut is fused with armor of brass, iron, and other mechanical parts. Oh yeah and their blood is molten fire, so have fun trying to chainsaw that rampaging daemon bull in half.
Khorne may gift a particularly effective unit of Bloodletters with Juggernauts to ride into battle; these units are called "Bloodcrushers." Similarly, particularly favored mortal followers (at least in Fantasy) occasionally get Juggernauts, becoming "Brass Knights" or "Skullcrushers." Lords or Heralds of Khorne leading an army may also do so mounted on a Juggernaut or a Juggernaut-drawn chariot.
Of course, Khorne doesn't just give them the reins; he allows them to enter the corral where Juggernauts live when they aren't killing things, and to choose one of them as a mount, but they are expected to tame it themselves if they wish to use it.
Note that the same units exist in both Warhammer 40,000 and Warhammer Fantasy Battle, because both use the same or similar realms of Chaos.
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The old Juggernaut model, heavily converted. If it weren't for the Berserker and it being a bloodthirsty daemon, it'd be kind of cute.
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The new Juggernaut model. Looks epic as fuck.