Anrakyr the Traveller
Anrakyr the Traveller is the former Necron Overlord of Pyrrhia who, upon reactivation, decided to renounce government over it and started to travel the galaxy along with the Pyrrhian Eternals to help reawaken the Necron Tomb Worlds which were still dormant, fighting possible interlopers or avenging destroyed Necrons if they were overwhelmed before he could help them. Think of him like a Necron Gandalf.
While he is utterly ruthless whenever he finds a lesser race sacking a dormant Tomb World, he has shown to wield a code of honour and spare the defeated enemy, offering honourable terms of surrender and even, perhaps, a sort of compassion.
For example, there is this short story in the codex where he captured a defeated IG colonel. He was supposed to hand him to Illuminor Szeras, most surely for painful and slow experimentation. When meeting each other in person (something which may not have been necessary), the colonel spit upon him, defiantly claiming that the Imperium would send more forces. Anrakyr, instead of handing him to Szeras, killed him on the spot. While this may have been to simply annoy Szeras for having used Deathmarks without his consent to win the battle, it may well be that Anrakyr didn't want the colonel to face a horrible fate as Szeras' guinea pig.
On the other hand, after saving the world inhabited by the T'au of Ka'mais, he and his army were greeted upon the ground with great cheering and celebration. However, being a Necron and also a grimdark badass, he harvested the planet on the spot, Thanos style.
Opinions of the Necron nobles over Anrakyr are divided. Most of them consider him an honorable warrior dedicated to help the survival of their race. Others (who won't give them the tribute of soldiers he requests from a tomb world after liberating it) consider him a menace as he invariably takes his tithe, even if he has to steal it.
Anrakyr also has technopathic abilities, allowing him to not only control his own forces, but also vehicles belonging to those who fight him. For example, in the story about his fight with the Imperial Guard mentioned above, he seized control of a Leman Russ Battle Tank, and, after briefly pitying its "flawed design holding back its full potential", made it fire its weapons on the remaining Guard forces. The most impressive display of this power turning the Silver Skulls Battle Barge Argent Hammer against them.
'Protip: "What's that, IG player? You say you brought a Deathstrike Missile Launcher? Can I borrow that for a sec? Thanks."
In the Silent King's Footsteps
7th Edition's "Shield of Baal" campaign had Anrakyr appear as he realized that the Tyranids in the Cryptus system just might eat up his timeshares. To this end, he woke up one of his tomb worlds called Perdita, hired out Zarathusa, the local Overlord, and then forged an uneasy alliance with Dante, Chapter Master of the Blood Angels, who was defending the Cryptus system from the aforementioned Hive Fleet. The crux of this deal worked upon some weird Necron made archaeotech on one of the planets, which allowed the Necrons to harvest the solar power of the twin suns of Cryptus and convert it to energy. If they could convert this, they could manage to find a way to detonate a gas giant and obliterate most of the hive fleet. Issue is, that involved their C'tan Shard using said archaeotech to power up the device so much that it blew up and incinerated not only the Hive Fleet but also most of the system, nearly killing the Flesh Tearers and Blood Angels Anrakyr was allied with while he just warped back to his crib.