Juggernaut

Goddamn, look at that thing. (note: this is an old Juggie, but it's the best we found)

Not to be confused with the X-Men villain, bitch.

A Juggernaut of Khorne is a daemonic steed, shaped roughly like a cross between a dog, a rhino, and a bull, and fused with armor of brass and iron and other mechanical parts.

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". A Herald of Khorne leading an army may also do so mounted on a Juggernaut or on a chariot drawn by Juggernauts.

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.