Kheldian
Much of this article is copied with permission from Memphis Bill's Kheldian Backstory guide 1.0. As such, it may contain an informal tone, and more references to how players can roleplay than other articles.
Overview
Kheldians are an alien species that was introduced to the game as part of the backstory for heroic "Epic" Archetypes. The playable Kheldians are Peacebringers and Warshades; the villainous Epic Archetypes are Soldiers and Widows. These archetypes are intended to have their own storyline, or "epic," to follow from levels 1-50; to that end, they have special contacts and missions that are unlocked as players level up. Because of the archetype-specific storyline, players that wish to roleplay a Kheldian accurately according to the game lore have less freedom with a character's backstory than other archetypes. Kheldians are also designed to be a "jack of all trades" style of archetype. Because of this, they are locked in to two powersets that have many more abilities than traditional powersets, and give players different shapeshifting forms to choose from. The changes to their powersets and especially the different forms give the Kheldians a significantly different play style from other archetypes.
Description
Kheldians are energy beings from outside our galaxy. They have the ability to join with human hosts in a (usually) symbiotic relationship. When this happens, the two separate personalities merge into one new one with its own identity and name. There are three types you'll typically encounter in the City of Heroes universe: Peacebringers, Nictus and Warshades.
Peacebringers
Peacebringers are, in essence, the armed forces of the Kheldian population, and are dedicated to hunting down the Nictus.
Nictus
Nictus were the ruling class of the Kheldians, known at the time as Science Lords, who started feeding off of the rest of the Kheldian population after scientifically altering themselves.
Warshades
Warshades are Nictus who, per the Kheldian lore guide, were "horrified" at the plans of the Nictus and turned to fight against them to defend Humanity.
Lifespan
The native lifespan of a Kheldian is from 10-20 years, per the original Kheldian lore bible. It is noted that reproduction can lower that.
By joining with a series of hosts, the lifespan can be extended near-indefinitely.
Host Relationship
When merging, the Kheldian and the host merge to form a new, combined entity.
The Kheldian's lifespan is extended, as is that of the host, who also gets new abilities.
A Nictus can take over an unwilling host, if the host's willpower is low. A host with enough willpower can keep control or force the Nictus out.
Only one Kheldian at a time can inhabit a host.
Forms
Natively, Kheldians are primarily energy beings with no defined shape. The Kheldian lore bible does mention them forming a "shell" and interacting with material items via tentacles formed of energy.
Nova
The Nova form is a tentacled creature with ranged attacks and inherent flight.
The Bright Novas are from their native gas giant's upper reaches, and are called Mefnanim. The Dark Novas are from the depths of the same planet, and called Hulmanim.
Dwarf
The Dwarf form is a higher resistance, tank type form with primarily melee attacks.
The White Dwarf form's native race name is Kurukt, living on neutron stars. The Black Dwarf form is named the Ruktur, living on the surface of a pulsar.
Leadership
Peacebringers
Sunstorm is the primary liason and contact for Peacebringers. He appears in Atlas Park. He explains, however, he is not in a leadership position. Moonfire exists in Striga Isle. She is also not part of leadership.
The Kheldians have a ruling council, but do not refer to them.
Nictus
Arakhn is the de facto leader of the Nictus.
Requiem is apparently equal to her in rank, and has led the Fifth Column since it was given to him by the Center in 1938.
Warshades
Shadowstar is not the leader but a helper similar to Sunstorm.
How long have they been here?
The Nictus have been on Earth for several thousand years. The Peacebringers are very recent arrivals, coming in at about the same time as the first Rikti invasion of Paragon City.
Not Quite Kheldians
Let's break these into three levels:
Quantum Gunners
Quantums are nothing more than your average bad guy who is armed with a Quantum Array Gun. These smack Kheldians rather hard, but other than that, they're just a thug.
Galaxy Troops
Galaxy troops are soldiers who have been infused with Nictus fragments ("pieces" of dying or weakened Nictus, though it seems healthy ones can create them too.) They are given some Warshade-like attacks (such as Ebon Bolt and Gravimetric Snare.) Not all of them are volunteers.
Galaxy troops can opt to go for a "full conversion" after a while to a full Nictus - most likely, given other in game comments, because the shards integrate more fully into the host, get stronger, and keep making the suggestion (plus the "longing for space" that's mentioned.) It's mentioned in a story arc that the conversion rate for Galaxy troops to full Nictus is reaching 40%.
Void Hunters
Void Hunter mercenaries are the real baddies, as far as Kheldians are concerned. They're infused with far more Nictus fragments which have been modified with Quantum energy and are out hunting Khelds. They have a Quantum Array gun, as well as additional Nictus damage when in melee that affects the Kheldian inside the host. Their altered fragments provide them with energy resistance, instead of the attacks the Galaxy troops get.
Arakhn's in charge of the Void Hunter mercenaries, though Requiem's secretly been sending "loyalists" to undergo the process. (Shadow Science.)
Others
Two other types of creatures come up in conversations about these - War Wolves and Vampyrii. Failed Galaxy conversions can create War Wolves, though there is also some separate process geared specifically towards making them. Vampyrii are made in a completely separate process that has nothing to do with Nictus shards or Kheldians at all.
There is a portion of the Kheldian story arcs that has you dealing with "shadow" enemies - Shadow freaks, Shadow Vampyrii and the like. These are Freaks and Vampyrii that have been infused with Nictus fragments. Nosferatu himself was considering it. But the fragments have NOTHING to do with the original creation of Vampyrii.
Names
Of course, part of the fun is naming your character. There are no hard-and-fast rules about Kheldian naming. Everything I thought I found for Peacebringers had some exception. I THOUGHT the name would be "solar object + light reference" but that's broken by Sunstorm, Moonbow and Freeflight... so go nuts. Warshades SEEM to have a "shadow" reference to them - but people seem to go that way (shadow/dark) with them as it is, given their dark coloration in-form.
The names, by the way, are the names of the joined beings. Shadowstar's daughter Lilian is slated to become "the new" Shadowstar, so it's an inherited name or title.
Native Kheldian names? We know of some - Altered Umbra, Perihelion, and Dirge of Entropy. The best "explanation" for these names is it's the best fit our minds and language can come up with for Kheldian names. They are, after all, energy beings.
Some names from within the game:
Peacebringer: Sunstorm (Kheld named Perihelion,) Freeflight, Moonfire, Coldstar, Fullalbedo, Moonbow, Brightshift
Warshade: Shadowstar, Shadowcatcher (Nictus named Altered Umbra), Romulus
Nictus: Requiem (Nictus named Dirge of Entropy,) Arakhn
So just pick something that sounds good to you.