Lazarus is the current Master of the Dark Angels Chapter's 5th Company and is their contribution to the initiative of making new characters that cross the Rubicon Primaris. He appeared in the September 2019 issue of White Dwarf before he got his full rules in Psychic Awakening: Ritual of the Damned.
Lazarus was a sergeant by the time Magnus the Red decided to nuke some yiffs. He won some renown here by helping lead the counter-attack when the forces of Chaos tried to storm The Rock. At some point after the Circatrix Maledictum ripped the galaxy a new goatse hole open, the 5th company's captain, Balthasar of Dark Vengeance fame, had fallen in battle and Lazarus was elected to take his place.
He swore vengeance for this insult and got his chance shortly after when Magnus tried to conquer the Stygius Sector. This went mega-terribly as the sorcerers all went mindfucky on him. His injuries proved so serious that his only chance of survival was to become a newer, better breed of Space Marine (Yes, as stated in his white dwarf article, he was so wounded that a dreadnought would not save him but somehow being turned into a Primaris marine made him better). This would mark the first time a Primarine entered the Inner Circle, though it was handwaved by the fact that he was already in the organization beforehand.
Once he was back in action, he was then assigned to visit the Grey Knights in the sector in order to confirm that the sons of Titan didn't find out about their big bad secret and find out just what they dug up. The 5th company (with assets from both the Deathwing and Ravenwing) and the Grey Knights under Brother-Captain Arvann Stern coordinated an assault on Sortiarius to disrupt Magnus' big rate-up ritual on Psykers. Lazarus' forces were tasked with drawing out any forces they could from the great temple of Tizca so the daemonhunters could do their job. They managed to draw out a lot of attention and lost a lot of troops, but they were duped into falling back. They eventually managed to group up and then tried opening fire on Magnus himself. In the end, all that could foil the ritual was an orbital strike. What forces remained fought their way to their fleets, though it was clear that they had left behind some survivors, damning them to death.
While he looks familiar, acting as a Primaris Captain with all the rules involved, this is where his wargear steps in to differentiate him. His sword is the Emnity's Edge, which is a dangerous S+2 AP-4 D1d3 that can re-roll to wound and the damage rolls when fighting an enemy psyker. He also has the Spiritshield Helm, which houses a special force field to all models within 6" that can potentially negate mortal wounds. His last special rule is Intractable Will, which lets him make some final attacks in melee in the event that he goes down.