Unfortunately much of the game’s lore is hidden within the Grimoire cards. Thanks to Reddit user KentsFood, he’s compiled information & lore about the Fallen (mostly from the Grimoire), which you can read below.
The Fallen are ruthless scavengers. Brutal and uncaring, they arrived on their massive Ketches in the wake of the Collapse to loot and pillage the devastated worlds.
There are hints of ancient nobility to the Fallen—the scars of lost grandeur. The Kells of their scattered Houses still claim to be royalty, but they leave only grief and wreckage in their wake.
The Fallen are a dangerous race, fast and agile, skilled in combat and supported by robotic allies. They have stolen and raided the ruins of civilization across the solar system, and you must deal with them in order to reclaim the lost colonies.
They follow a strict hierarchy in soldiers, employing the lowest of the lows in society: Dregs. Dregs have their lower arms removed in a ritual of humiliation and obedience, they constantly seek to become the best of their kind, so they may ascend the ladder (and regrow their arms) to become:
Vandals. Vandals are the veterans; seasoned, experienced warriors who employ a variety of methods to end Guardians’ lives: Stealth cloaks, Arc blades, Wire Rifles, and any other number of horrifying weapons the vanguard have yet to encounter.
Captains are the top of the chain, the commanders of Fallen units on the ground. Formidable, shielded opponents, they carry the banner of their house. Ruthless, even to their own kind, they have been seen to kill lesser infantry for disobeying orders.
Note that a Baron is ranked even higher than a Captain, and if they are encountered should be dispatched with extreme prejudice.
Archons are Priests. Huge, hulking Fallen who are in charge of relaying the Kell’s orders to the Servitors. The Archon is believed to convey the Kell’s wishes to the Prime, who sends orders out to units across the Planet. However, it could be possible that Archons are merely subjects of the Prime’s will.
The Kell is the leader of the House, immensely powerful Fallen who should not be taken lightly.
Servitors are believed to be relics of the once mighty Fallen civilisation. They process matter and energy into Ether, which the Fallen need to survive. They support Fallen with powerful energy weapons and defensive systems. Servitors are attached to a Prime Servitor, a huge Servitor in symbiosis with a Fallen Archon.
While the Kell are political leaders of the Fallen, A Prime Servitor is believed to be more like a God. Recent developments suggest that the Prime Servitors are involved in Fallen star flight.
The Fallen employ Shanks, a hovering robot that scouts, patrols and guards important areas for the Fallen militants.
Walkers (also known as Spider Tanks) are giant, six-legged robotic tanks that are placed in key positions to protect Fallen leaders and destroy enemies of said leaders. Guardians are warned, these machines are not to be take lightly. Their tracking system accounts for multiple targets as their giant cannon locks onto threats with terrifying accuracy.
During the Battle of the Twilight Gap, Walkers are reported to have engaged in explosive battle with the City’s gun positions.
Pikes are the Fallen’s patrol vehicles. Lightning quick with twin cannons of deadly arc energy, Guardians are asked to capture these devices where possible. Their use in the Crucible is paramount for our training.
The Fallen are split into several Houses, each of which seem to have a separate agenda.
The houses have not seen to be united since the Battle of the Twilight Gap, where all the Houses united in a full assault of the City.
The House of Devils is the primarily encountered House on Earth.
The Devil’s led the charge at the Twilight Gap, and are a consistent threat, and it would not be to bold as to say the biggest threat, to the Guardians and indeed, to the fate of the Earth.
They are noted for their red clothing and constant presence in the Cosmodrome, where it is believed they are searching for something buried deep in the ground. It is worried that whatever they are looking for could prove the City’s undoing. No records of the Devil’s Kell exist, however, Guardians have defeated Riksis, a Devil Archon. Riksis was known to collect the skulls of dead guardians as trophies. His death is great relief to the Vanguard. The Devils’ Prime Servitor: Sepiks was defeated by a fire team in the Devil’s Lair on Earth, by order of Zavala. Sepiks’ destruction will prove invaluable in the fight against the House of Devils.
Encountered on Earth upon the discovery of Rasputin, the House of Kings in their banners of Gold revealed themselves. Nothing much could be found in the records of this House. Be watchful, Guardians.
On the Moon, Guardians have encountered the House of Exile. Not much is known about this house, but due to it’s abnormally large populace of Dregs, it is suggested this House is new, perhaps gathered from the outcast of the other Houses. If this is true, this house is a threat. Such need to secure themselves amongst their kin could drive them to extreme actions.
Venus is home to the House of Winter, draped in blue. They seem interested in the Ishtar Academy on the Shattered Coast, but may redirect their efforts into the Citadel. The House of Winter was lead by Kell Draksis, an elusive target for the Vanguard. Cayde-6 personally raised the bounty on his head. The Kell was defeated by Guardians, who stormed his Ketch and slay him in his throne room. Such a defeat could prove chaotic to the House. Winter’s Prime Servitor, Simiks, is reportedly dead. A Servitor called Simiks-3 was encountered and destroyed by guardians, and was believed to be created from the remains of the Prime.
A note at the bottom of Simiks’ information read: “Evidence of it’s demise remains elusive.”
Little is currently known of The House of Wolves, save for that they believe the Queen of the Reef to be their Kell. It is unknown if the Queen destroyed their previous Kell and took the mantle herself, or if she knows something about Fallen politics the Vanguard don’t.
Aksor is a Fallen Archon under the discipline of the Prime Servitor Kaliks.
Aksor lead assaults on settlements beyond the City and ravaged Awoken enclaves in the Reef. The Queen was able to capture Aksor and seal him inside the Prison of Elders. However, The House of Winter raided the prison and freed Aksor, seeking to force him to join the ranks.
They succeeded, but Aksor was killed by Guardians before he could fully realise his destruction upon humanity.
It is possible that both Aksor and Kaliks belonged to the House of Wolves prior to their acquisition by the Queen.
Cayde-6 recorded an interesting story of a female House of Exile Baron aiding him in combat against the Hive on the moon. The ending undoes any sense of comradeship between our races, but the sentiment is there.
A document titled: A ROUTINE SUMMATION OF DARLINGS WON AND HEROICALLY HELD DURING THIS PROFITABLE CYCLE, AS COMPLIED BY A DREG was uncovered as well. The document outlines several materials and stories gained from a “profitable cycle.”