Ollanius Pius
The most hardcore Guardsman ever to walk the earth and also the legendary saint of the Imperial Guard. Ollanius Pius put himself directly in front a walking god of battle who has just ripped apart a Space Marine Primarch in the hopes of protecting the Emperor of Mankind. The fact that he did so without fainting, shitting himself in terror, or mewling like a wounded grox suggests that his testicles must have been forged from Mars-grade Adamantium. His death proved that Horus had given himself over to chaos completely; and with this in mind, allowed the Emperor to lay down a righteous psychic asskicking strong enough to rend his former son from existence by destroying his very soul. Yeah it was that fucking manly.
Naturally, like so much other awesome shit, Games Workshop has retconned him out of existence (first replacing him with a Spehss mahreen Terminator, and then an Adeptus Custodes) which is SIX KINDS OF LAME. FUCK YOUR CONTINUITY, GW.
Other then the fact that he was man enough to stand-up to daddy's favorite with nothing more then a flashlight and toilet paper armor, not much else is known about him, except that he is a legendary saint of the Imperial Guard, and that's still rings true even after GW replaced him with a Terminator and a Custodes. Which probably means that he did even more heroic and manly shit during the Siege of Terra and everything else leading up to the final battle on Horus' flagship.
A small piece of writefaggatory that explains Ollanius
From some guy in /tg/:
LOOK AT THIS FUCKING GUARDSMAN.
He's spent months fighting a grueling war in which his enemies are demigods allied with daemons, and now he's found himself in the closest thing to Hell he's ever known. He probably wasn't even supposed to get teleported up to the arch-traitor's battle barge in the first place, and just ended up in the wrong place at the worst possible time.
Somehow he's survived horrors beyond comprehension to make his way to the very bridge of Horus' flagship. He saw a veritable angel call upon Horus to answer for his crimes, and he saw that angel die as messily as any guardsman. His Emperor - who he fervently believes is a god incarnate, even if he's not supposed to - lies mortally wounded, and Horus, perhaps, has taken a moment to gloat before he strikes the killing blow.
His armor is slightly more effective than tissue paper, his weapon is slightly more powerful than a flashlight, and Horus' power claw is bigger than his entire body. He stands before a being infused by the dark gods with incalculable power, that can and will obliterate his soul with no more effort than it would take him to swat a gnat. Nothing he can do could possibly make a difference.
He could run. He could turn his weapon on himself. He could give in to the insidious whispers that echo from the ship's corridors into his mind.
Ollanius Pius does the duty his Emperor requires of him. He dies standing, and holding the fucking line.