Varro Tigurius
Varro Tigurius is the most powerful human psyker ever (allegedly). And he belongs to the Ultramarines. Who
would have thought? He is so powerful he can beat daemons like a Grey Knight, he can fight like a Terminator, use every known psychic power (and several unknown ones) AND foresee the Hive Mind's plans. Somehow. It is worthy to note this is the same Hive Mind that blots out a psychic power on par with the God-Emperor of Mankind Himself. How one man can use the warp against this is unknown.
In spite of all this, the Daemonculaba still gives him nightmares.
Also did we mention this was BEFORE Matt Ward wrote him?
In game, think of him as a psyker that will mind rape everything. Then double whatever first impression you have and then you have a good idea of his prowess.