The Risen (Dark Angels)
The Risen are a faction of Dark Angels. Formerly part of the Fallen, they now faithfully serve their newly-returned Primarch as part of his forces in the Lion's Protectorate. They serve as his bodyguard and entourage, though they also serve as his emissaries and field commanders if the need arises.
History
The Risen were unofficially formed when the Dark Angels Primarch Lion El'Jonson woke up from his 10-millenia nap and vision quest, and found how much the Imperium, ESPECIALLY the half he had woken up in, had gone to shit in the time he had been asleep. Though it started with just Zabriel, by the Lion's own decree it is open for all non-Chaos aligned Fallen to join, and since then has grown to almost a score or so Heresy-era veterans.
This... is not a lot, and as more worlds join the Protectorate, the Risen are already feeling the pressure as their force is getting spread thin across all these worlds. And while Zabriel is trying to court more of the Fallen to their banner, their numbers are still nowhere near enough to challenge the apparently Legion-sized number of Chaos Fallen now gathered under Luther and the Daemon Prince Marbas. (Which in hindsight is amusing given Luthor has said he will only ever recant to the Lion himself, and that he had constantly rants and raves about the Lion coming to absolve the Fallen-which is exactly what seems to be happening. Perhaps this is a trap by Luther to gather all of the chaos-aligned Fallen in a single place for them to be wiped out in one fell swoop? We will only know if GW ever finds out how to complete plot lines without pissing off the general public.)
This isn't as weird as it may seem at first-by this point the Lion and the Fallen likely have more in common with one another in terms of history and beliefs than the modern Dark Angels do with the Lion, and so pragmatically offering the carrot when possible instead of the Dark Angel's previous policy of just stick may be more fruitful in the long run.
Though many joined for their own reasons, they are all loyal to the Lion and the Imperium, regardless of what the modern Dark Angels feel about the matter.
Notable Members
Zabriel -- The first Risen, and unofficial emissary of the Lion to seek out and invite other Fallen to their cause. Terran-born from what was once Stockholme, he was once a member of the Dreadwing, and still wears their symbols, and a veteran of the Rangdan Xenocides. After the destruction of Caliban he was spat out of the Warp 400 hundred years ago, and had since then been lying low in the Imperial world of Camarth. For all his resentment of the Lion, Zabriel was still loyal to the citizens of the Imperium, and when the Great Rift happened and Camarth got stuck in Imperium Nihilus, he did what he could to save them when Chaos came knocking. When his merry band of refugees brought back a massive armored figure to their hidden camp, Zabriel attacked on instinct. Naturally the Lion knocked him flat on his ass. After several hours of hear-to-heart talk with his dad on the current state of the Imperium and how many of the Fallen had gotten a bum deal for 10000 years, the Lion asked him to serve him once more and help reclaim Camarth for the Imperium. Much asskicking followed, and Camarth became the first world to become part of the Lion's Protectorate, and Zabriel embraced his role of spokesperson for the Lion in bringing in his other wayward sons.
Lohoc, the Red Whisper -- An intensely private former Fallen, Lohoc is considered... strange, both in-universe and out. Meta-wise, he actually showed up as part of Cypher's merry band of Fallen in Rise of the Primarch (though there he was only known as the Red Whisper). In-universe, no one is really sure if he's even a Dark Angel to begin with, as even the Lion, who could remember many individual members of the Fallen, had no idea who he was. What's worse is that he declines to ever remove his helmet, even after the Lion forgiving him and then asking nicely about it, pointing to either a bad memory or a particularly obvious case of Chaos mutation (though the Lion says that he allows for... some eccentricities for the Fallen who rejoin him). His loyalty is unquestionable though, and prior to the whole Rise of the Primarch thing was apparently hunting down Chaos beasties preying on the Imperium in the Lion's name.
Borz -- Former Knight-Captain, the first thing that Borz did once he got spat out into the modern Imperium after the fall of Caliban was form a pirate fleet under his command. Naturally charismatic and utterly ruthless, Borz would gather other Fallen to this banner (spefically Perziel, Rufarel, Cadaran, and Breunan), gave them command of warships and mortal crews, and wreaked havoc on Imperial shipping lanes, even coming into conflict with other Fallen and Chaos-aligned marauders. When the Great Rift opened, his fleet found itself in the ass-end of Imperium Nihilus, but when an astropathic message was intercepted that claimed that the Lion was on the Imperial World of Avalus, Borz gleefully led his fleet there. When he found the world under siege by a Chaos fleet, he led his pirates against it. Once he met the Lion personally in the aftermath of the battle, Borz made no excuses for what he had to do to survive, but now he was willing to follow the Lion's leadership once more.
Arthurian References Ahoy!
Many of the named Risen are references to King Arthur's Knights of the Round Table -- specifically Ector, Lancelot, Percival, Bors, Galahad, and Bedivere. Though it still begs to be seen if they'll completely mirror the Knights that they references, but that's a possible Black Library story on its own right?
So where are their rules?
Most players would assume that rules for The Risen or that Dark Angels 10th Codex would be released before or at the same time as the Space Marine or Dark Angels Codex. Maybe they might even get Datasheets on Warhammer Community.
Compounding players frustrations, The Fallen were removed in the 9th Edition Codex, and this was after being effectively relegated to a White Dwarf during 8th. So we have no idea when or if they'll even get rules at all.