Kalagann of Ursh

Lore;
Kalagann of Ursh is a brutal despot warlord who rules over a barbaric kingdom among the radioactive wastes of Old-Terra. Ursh is a terrible, broken place, remembered in belived-fictional writings in the 41st millennium. He revels in destruction, and seeks not to improve the lives of his subjects. Instead it is only the reduction of his enemies that he seeks. Kalagann of Ursh is the sacker of the great caterpillar cities, enslaver of psyker-sorcerers, and heir to god-like technologies. He is the symptom and cause of mankind's downfall, one of the great festering sores of Old Night, when humanity regressed to its darkest instincts. It took the God-Emperor of Mankind to defeat this abomination, will you adventurers stand a chance? Or add your lifeblood to the toxic soil?  

Wargear;

Armor of Pearl: The armor of pearl is a masterwork set of artificer armor with a built in refractor-field that disperse all incoming blows to harmless pearlescent light. This armor is unspeakably ancient, from the Golden Age of Technology, and Kalagann powers it with a crude warp-engine bound to 8 psychers, his Storm Dogs who march into battle with him. While this refractor field is active there is hardly any technology or magic that can harm Kalagann. In addition this armor grants him great presence on the battlefield, injecting him with combat stims, and augmenting his physical capabilities. In rapid bursts of strength the armor can even break the sound barrier and compress air into shock-waves as it moves. 

Gore-Cleaver: A brutal poweraxe, with a specially tuned field that boils and irradiates blood upon contact turning each kill into a toxic gory explosion. Kalagann himself is protected from this horrid spray by the Armor of Pearl which transforms the grotesque detonations into dazzling light displays where they spray against Kalagann's armor. 

Storm's Fang: Another technological marvel, a volkite pistol. This thermal-lance weapon is capable of projecting deadly beams out to 200 feet through even the toughest barriers and armor.

Storm Dog Pack: There are 8 of these lobotomized psyker-sorcerers who Kalagann has had lobotomized, and then psychically chained to his armors warp-engine. They howl and rave at all before them projecting warp-storms (Prismatic Spray), and spouts of warp-fire and mutagenic blood (Cloudkill). They also seem to be able to  teleport terrible warped abominations from Kalagann's cells onto the battlefield, these creatures are warped pathetic things no longer recognizable as human, changed through gene-experiments and warp magic (Summon Fiend). 

How to play: Kalagann of Ursh seeks bloodshed above all else. He will use his Barbarian charge, and leap to close distance as fast as possible, attempting to destroy hostiles with the Storm's Fang pistol if he isn't able to reach melee range. The Storm Dog Pack will usually begin by summoning a gene-horror with Summon Fiend. Kalagann trusts the Armor of Pearl completely, and will be largely headless of danger when engaging. He will not hesitate to execute downed foes, and will attempt to secure at least one kill if the battle begins to swing against him. He also never walks on the field of battle alone, even beyond his Storm Dog Pack Kalagann of Ursh fights alongside his terrible armies whether on a raid, or defending his kingdom.

40k/5e;

This creature is designed for the Warhammer 40k universe, and thus is a bit of a different flavor than most other high level creatures in Dungeons and Dragons. This creatures power come from lost technologies, and the strange powers of the warp, rather than the powers of the planes and the weave. To portray this creature in the flavor of its original universe add drama and horror to every description. Remind the players that this monster is using pinnacle technologies of a golden age the same way a toddler uses a shovel to smash a sandcastle. The magic Kalagann employs are all psychic energies from the warp, which always come with danger to employ. Although he does not know it Kalagann has attracted the attention of Khorne who sends him aid in the form of the expulsions of power unleashed by his Storm Dogs. 

The only material in this statblock that are official canon are the existence of the Armor of Pearl, and that Kalagann lead an old-Terran brutal empire known as Ursh. Most of these references can be found in scattered references across the Horace Rising novel (pgs 180, 229-231). The majority of the rest was inspired by the "40k Lore: Technobarbarian Lords and Their Forces - Deep Dive!" video by D_Storyteller_P13, and with help from PeterHolland1 on Reddit.

Blood Rain.

The land of Ursh is a radioactive blood-swamp maintained by the warp-storms that persist over Kalagann's lands. 

All creatures in Ursh take 2d4 acid damage at the beginning of each of their turns, and all earthen ground is transformed into difficult terrain. 

Lair Actions: 

Drown In Blood. Kalagann attempts to drown a creature in the toxic muck of Ursh. Melee Attack Roll: +19, reach 15 ft. Hit: 15 (1d10 + 10) Bludgeoning damage plus 14 (4d6) Poison damage. On a hit the target is grappled, and begins to suffocate for as long as they are grappled.

Mental Malaise. The strange energies that permeate Ursh can infect the mind of even the most stalwart warrior with unending blood-rage. Using Spellcasting Kalagann of Ursh casts Crown of Madness.

Red Engine Artillery. (Recharge 5–6). At a vox-signal Kalagann of Ursh orders massive cannons to fire upon the battlefield. Each creature in a 20-foot radius from a point within Kalagann of Ursh's line of sight. Dexterity Saving Throw: DC 27, Failure: 84 (8d10+40) Bludgeoning damage. Success: Half damage only.