Hive Tyrant

A Hive Tyrant is the scariest possible thing an Imperial Guardsman will ever have the misfortune of seeing. Mostly because it will be the last thing he sees.

Hive Tyrants are the largest of the Tyranid Synapse-Creatures, making it three or four times the average human, all of it violent muscle, claws, and teeth able to tear through plasteel, ferrocrete, and ceramite with ease. Unlike other Tyranids, Hive Tyrants unique entities in the Hive Hind, meaning that if actually do manage to kill the thing, they're not only coming back, but they're going to be seriously pissed off.

At least that's what the fluff says. On the tabletop, the Hive Tyrant has some interesting psychic powers, but is massively expensive, lacking invulnerable saves, and can't join squads.