Marneus Calgar, in all his chavness.
Marneus Augustus Calgar (also known as The Notorious M.A.C, The MAC Daddy, Margayness Cockguzzler, and Pimp Daddy Calgar) is a character from the fictional Warhammer 40k universe. According to Matt Ward, 5th edition codex writer, Calgar is the spiritual liege of every Space Marine ever. All the Space Marines look up to him and strive ever jovially to be more like him and his Ultramarines, but because of their laughable shortcomings, most Chapters, including the Dark Angels, White Scars, Imperial Fists, Blood Angels, Iron Hands, Salamanders, Raven Guard, Space Wolves and all their successors, will never be as good. It is stressed constantly in the vanilla Space Marine codex and even mentioned a bit in the Blood Angels codex. The entirety of the Imperium awaits the day the Emperor awakes so that the Emperor may proclaim Calgar the rightful heir to the Imperial throne. As a surely irrelevant side note, Matt Ward plays Ultramarines.
Calgar back in ye olden days. Note the Beakie
Marneus Calgar is the current Chapter Master of the Ultramarines Chapter of Space Marines, and titled Lord Macragge. Following a skirmish against the Tyranid Hive Fleet Perseus in 976.M41, Calgar lost all four limbs as well as large areas of body tissue and his left eye. Now fitted with bionic replacements, he is more machine than man. Several fa/tg/uys have argued that he currently bears a prosthetic robotic penis .
And here is that old image in model form.
Calgar is one of the big three, the others being Dante and Logan, the three Chapter Masters the whole Imperium knows. While Dante is worshiped as a larger than life legend. Logan is beloved for being a bro to the common man, Calgar is repected for his leadership, both in battle and ruling Ultramar.
His characteristic weapons are the Gauntlets of Ultramar, which were reclaimed by the Primarch Roboute Guilliman from a Chaos Champion. These gauntlets allow Calgar to bash gaping holes in enemy lines, allowing his men to achieve victory for the Imperium in a joyous slaughter of the heretic forces across the galaxy. They do, however, make it extremely difficult to use restroom facilities, turn door handles, or hold small objects.
An unofficial nickname for Marneus is "Papa Smurf", due to other players referring to the Ultramarines as Smurfs and Calgar being their leader. The nickname has its origin in the actual miniatures' diminutive size and the fact that they are blue. One could also point out of course that the average cartoon smurf is either a total dick or pants-on-head-retarded, and requires Papa Smurf's constant leadership and guidance just to function on an everyday basis. This allows us to extend the metaphor in a hilarious way.
As of 6th edition he is also a xenos-loving bastard, having allowed the Tau to evacuate a planet that was facing Exterminatus due to a Tyranid infestation. To be fair, though, the Tau are one of two races (the other being Eldar) who work with the Imperials at points, so this could be just a bargaining chip to be used later.
He Also duel wield Necron Pylons while the Ultramarines were retaken Danmos.
 On the Tabletop
It's just a flesh wound. He still deals with it better than a certain armless failure
Calgar is your typical "cost more than a Land Raider" HQ choice, he's a Chapter Master with Eternal Warrior, the Gauntlets count as two power fists and a storm bolter with AP 2.
But his stats in Combat aren't why he's of use.
Calgar can allow the entire Ultramarine force to choose to pass of fail any moral test they may make. As well as using a Ultramarine combat doctrine twice, as well as rolling the Warlord trait three times and pick the one you want. Allowing him to be one of the most tactical flexible HQs in the Codex.
So while costing a ton he's well worth it for what he does for your army.