My first build post, so please be kind 
Update Jan 2021 and 1.1.8.1: Some minor tweaks to make farm-running a bit faster, and my very first video upload.
Intro
I’ve always been a fan of the sword-and-board holy warrior (paladin, in D&D) archetype, and after becoming a fan of the base Grim Dawn game, I purchased AoM and FG and then created my third character as what seemed the natural combo of Oathkeeper (shield offence) and Soldier (shield defence). So early into my game experience, I didn’t know about the many guides to follow, and was wholly reliant on Sir Spanksalot’s excellent (but dated) guide to devotions. So I won’t pretend this is even close to the perfect retaliation warlord - I think that would still have to be Maya’s famous Drunken Fwuffy. Maya’s build is perfect… but perfection can be really hard to obtain; you both have to (a) get there and (b) find the right gear; particularly levelling “honestly” with only two level-50s preceding at the time it wasn’t an option. Even with 10 level-100s and 2000 hours of play later, I still don’t have all the gear Fwuffy requires. You pretty much have to spring forth born perfect, like Athena from Zeus’ forehead.
Like I said, this build is far from perfect; it’s a result of muddling ahead and discovering the game as I went along, relying purely on self-found gear, and the rare lucky find of epic items in the process. Early build was reliant upon the Soldier’s level 15 Guardsman set, which is forcewave/defence-focused, and good for those early levels. But while there is a level 65 version (plus the level 50 Praetorian set along the way), my experience was that FW/shield really falls off around 40. But a chance set of drops gave me parts of the Perdition set, and there are both Empowered and Mythical versions that can take you all the way to level 100, and are relatively easy to obtain (particularly if you make use of the Transmutation lottery). Late-game ancillary items that give %retal to attack skills are desirable, but not necessary. While levelling pre-Ultimate, Spined Carapace augments are very helpful.
Mechanics
The build (GT link) emphasizes overwhelming defence (is that an oxymoron?) with with 3.1K passive DA, 5765 armour, nearly-constant 4077 shield block (88%) , and very high block recovery (57% without Overguard, 100% with). DPS is 71K (RF+Aegis) but passive OA is a laughable 2.2K - but keep reading to see why this is OK. Burst OA can reach 2344 (Ascension) and armor/shield can rise to 8282/5936 with stoneguard+overguard. Most damage is done by straight passive retaliation (168K across multiple categories, nothing is immune). Active damage is predicated on %retal-to-damage skills like Righteous Fervor, with Aegis of Menhir interspersed. The low OA is acceptable since you don’t really need it for retaliation, and you are actually OK with the minimum-to-hit-60% mechanic (which is normally seen as a token gift to enemies, but here we knowingly accept it as an offensive floor). Since the build is always going to be blocking, Targo’s Hammer (Anvil) and Trample (Autumn Boar) are added to the mix. Sustainability is enhanced by Stone Form devotion, Stone Guard boots. Menhir’s Will, Dryad and the occasional healing potion more than keep up with damage received, mostly the brief intervals when Overguard is down.
Performance
I’m not going to post a Youtube link to Ravager takedown, because you’ll all fall asleep watching her flail away at the flesh-eating turd while hopping off blood puddles or soul swirls for 12 minutes, but rest assured it is possible, even trivial as long as the pilot doesn’t fall asleep at the keyboard. I don’t think the build can take Grava’Thul, but all other nemesis (nemesii?) are viable. Oddly, the toughest fight I’ve done with her is endboss trio in Valbury Ultimate, because they kept healing faster than she could damage them (since they were casters not triggering retaliation punishment). I never felt I was in any true danger, but I was afraid I’d die of keyboard-mouse fatigue. I have included a video of Fabius dying in 25 seconds (I was sloppy as I was learning the videocapture software, normally it takes about 15 seconds). Bearing in mind that Fabius is about the easiest Nemesis for this build to fight.
This is the only character I have who misses frequently and is missed frequently. If you see a critical from either side, it’s probably a sign from Empyrion that you should pause the game and go buy a lottery ticket.
This build performs well enough in Crucible (no video, sorry), but rather poorly in Shattered Realms (unbuffed SR 50 is certainly possible but a pain) because there are often too many environmental effects and traps in SR that neither shield block nor retaliation help with.
For regular game content, against regular mobs and some bosses and heroes, you can pretty much just ignore them - early game I was taking the time to read lore notes while ignoring the lemmings throwing themselves onto her spiky armor. In fact, this is my fastest location-farmer (e.g. the aether crystal run, or the Ugdenbloog stump run) because not only can you ignore things that can’t get through the high armor, but most things that even try, die without you touching a key. “Spitters” can require active intervention though; get Targo’s hammers going and run around in tight circles, spamming RF will do fine. Overguard isn’t actually necessary most of the time, except for bosses. Casters are the most obnoxious of opponents, but this build isn’t entirely helpless without retaliation / block; with an adequate, if slow RF autoattack.
But for the turtle, slow-and-steady wins the race.