Merek Grimaldus, the Hero of Helsreach, is the Reclusiarch of the Black Templars. He is also the single most stone-cold badass chaplain in the galaxy and he absolutely refuses to die. He is often accompanied by a posse of Servitors, and is really good at smashing Orks and slaying Tyranids. Grimaldus is so famously hardy and resilient that some (mostly guardsmen from Helsreach) have said he's immortal, though as it turns out he's just spectacularly good at not dying.
Also apparently not a huge fan of Sanguinala.
Grimaldus appears in the novel Helsreach, by Aaron Dembski-Bowden, where Grimaldus not only survives getting an entire temple crumbled over him but kills an ork Warlord with a single strike of his power mace, saves an Imperator Battle Titan princep from getting assimilated by her engine's spirit by merely demanding her not to fall, steals an Ordinatus from the Adeptus Mechanicus and has his Techmarine hack it so it can kill what was probably the biggest Mega Gargant of the whole Third war for Armageddon, gets his first human friend named Andrej, a steel legion stormtrooper with even bigger balls than the average Imperial guard, amongst other awesome feats. While Grimaldus is for a large portion of the novel whiny about the fact he has to fight for a doomed hivecity he eventually realizes that, more than defending a physical objective it is to keep the spirits of the Imperial defenders up that he is there, which is, after all, the job of a Chaplain.
Recently, however, he became best buds with Pride Leader (Sergeant) Ekene Dubaku of the Celestial Lions and set about in an attempt to save their doomed chapter from the wrath of the Inquisition (spess mehrine style!). He even called them naive for messing with the Inquisition because who in their right mind would? (The Space Wolves that's who!) Which further proves the point because half the chapter are bonkers and the other half are filthy furries, (which is completely true) but I digress; they got a lot of Ork assess kicked and got shit done in true Space Marine style. Now there is some hope that the Celestial Lions might survive. Shows how choosing your allies plays a huge part in this mess.
Prior to the Black Templars being mashed into the Vanilla Marines codex, Grimy had a unique special rule similar to reanimation protocols. Upon losing his last wound Grimaldus would make a morale check (ignoring the auto pass he would get from being fearless), if he passed he would fight on with one wound remaining. In the new Space Marines codex he was instead given It Will Not Die.
Being a Chaplain obviously means that you must rouse your men to perform acts of heroism. Grimaldus goes above and beyond that. This speech is from the previously mentioned novel Helsreach. Grimaldus, his Templars, and the Steel Legion stand in Helsreach while the Ork Horde gathers outside. The Defenders are nervous and worried and Grimaldus decides to motivate them the only way a Chaplain knows how to. For maximum effect, read this with the voice of the Chaplain from Dawn of War.
"Do you see that?"
(The Defenders are silent)
"I said... DO YOU SEE THAT?!"
(A few in the crowd says Yes sir)
(Grimaldus starts laughing maniacally)
"Are you all as insulted as I am? THIS is what they send against us? This RABBLE?! We hold one of the mightiest cities on the face of this planet. The fury of its guns sends all skyborne enemies to the ground in flames. We stand united in our thousands, our weapons without number, our purity without question and our hearts beating courage through our blood. And THIS is how they attack us? Brothers and sisters... A legion of beggars and alien dregs wheezes its way across the plains. Forgive me when the moment comes when they whine and weep against our walls. Forgive that I must order you to waste ammunition upon their worthless bodies. I have heard many speak my name in whispers since I came to Helsreach. I ask you now: Do you know me?"
(A few yes's are heard in the combination of Marines and Steel Legionnaires)
"DO YOU KNOW ME?!"
(Yes's get louder)
"I. AM. GRIMALDUS. OF THE BLACK TEMPLARS! A BROTHER TO THE STEEL LEGIONS OF THIS DEFIANT WORLD!"
(loud cheers follow but they aren't really that into it)
(Grimaldus kicks it up a notch)
"Never again in life will your actions carry such consequences. Never again will you serve as you serve now. No duty will matter as much and no glory will taste as true! We are the defenders of Helsreach! On this day we carve our legend in the flesh of every alien we slay! WILL. YOU. STAND. WITH. ME?!"
"WILL YOU STAND WITH ME?!"
(more thunderous cheering)
"Sons and daughters of the Imperium! Our blood is the blood of heroes and martyrs! They DARE tread the sacred soil of our world?! We will throw their bodies from these walls when the final day dawns!"
"THIS IS OUR CITY! THIS IS OUR WORLD! SAY IT! SAY IT! CRY IT SO THAT THE BASTARDS IN ORBIT WILL HEAR OUR FURY! OUR CITY! OUR WORLD!"
"OUR CITY! OUR WORLD!" - the defenders reply
(Grimaldus turns to face the horde of orks. Laughing)
"RUN ALIEN DOGS! COME TO ME! COME TO US ALL! COME AND DIE IN BLOOD AND FIRE!"
"BLOOD AND FIRE!" - defenders
"FOR THE TEMPLARS! FOR THE STEEL LEGION! FOR HELSREACH!"
"FOR HELSREACH!" - defenders
"FOR HELSREACH!" - defenders
(the shouts have broken the glass of several nearby buildings)
"THEY CANNOT HEAR YOU BROTHERS!"
"HELSREACH!" - defenders
"HURL YOURSELVES AT THESE WALLS INHUMAN FILTH! DIE ON OUR BLADES! I. AM. GRIMALDUS. AND I WILL CAST YOUR CARCASSES FROM THESE HOLY WALLS!"
"GRIMALDUS! GRIMALDUS! GRIMALDUS!" - defenders
On the Tabletop
Grimaldus is a killy, durable, debatably overcosted Chaplain. He's an independent character with the ATSKNF and Chapter Tactics: Black Templars (Crusader and Adamantium Will, plus rage and counterattack if anyone dies in the shooting phase), plus he gets Zealot, Unmatched Zeal (gives his unit the Zealot USR) and IWND, which is a bit of a nerf. It used to be that whenever he died he'd roll a morale test at Ld 9. If he passed he'd keep on with one wound, though he could only do this once per battle and would need to take Morale tests for every turn afterwards, dying if he ever failed (at least if gave him Instant Death resistance in an edition when practically nobody had it). His servitors can give FNP to every friendly unit (unit, not model!) within 12". His warlord trait lets everyone in his detachment use his leadership of 10 for all morale rolls. For gear he comes to war with a rosarius (apparently he had another one built), frag and krak grenades, a (surprisingly not relic) Crozius Arcanum he borrowed from his mentor Mordred (who is still annoyed with Grimaldus for this, despite being dead), a master crafted plasma pistol, and for some bizarre reason, power armor. The fuck? The guy is the Reclusiarch, keeper of the chapter's relics, yet he can't get a set of artificer armor?
Grimaldus is probably one the best chaplains in the game in terms of crunch and a godsend to people trying to play the fluffy "army of footslogging crusaders" templars army, though he can still do anything a typical chaplain can. He's reasonably killy on his own, though no more than any other chaplain, but the real reason you take him is to stick him in a foot-slogging crusader squad. Stick Grimaldus and all his servitors in a full crusader squad and you now have 30 T4 wounds on a unit that has FNP, Adamantium Will, Rage, Counterattack, Zealot, LD10, all for... just shy of 465 points. Okay, so it's not especially point efficient, but if you're trying to play oldschool footslogging Templars, Grimaldus is pretty helpful for that, and even for that many points, 30 wounds worth of space marines with that many special rules is nothing to sneeze at, and if you're fielding Helbrecht to call his WAAAAGH stand-in, you now have 64 attacks (10 marines, 10 neophytes, 1 attack base, 1 for 2 CCWs because of the chainswords you're taking, an extra for the charge plus the squad leader, plus the servitors), plus Grimaldus's attacks, coming out to a grand total of 54 attacks at S4, 10 at S3, plus 4 at S6 from Grimaldus, all of this rerolling because of hatred, though as previously discussed this is more fluffy than point efficient.