Are there any known examples of the chaos gods turning a non-astartes into a demon prince in warhammer 40k?
I know other Xenos races like the Laeren do worship them and they have normal human followers, but to the best of my knowledge only astartes and primarchs have become Demon princes.
As far as I know there isn't any reason why they couldn't but I can't think of an example.
Ingethel
Ingethel, the daemon that is "responsible" for the Horus Heresy, is actually a Daemon Prince from Cadia.
From Lexicanum,
Ingethel, also known as Ingethel the Ascended, is a Daemon Prince of Chaos. Ingethel was originally a native to Cadia and was appointed by the Gods of Chaos to guide Lorgar during The Pilgrimage. After Ingethel revealed the Primordial Truth to Lorgar, she herself ascended to Daemonhood following 10 human sacrifices
At that time, Cadia had been newly recolonized by the Imperium.
Before Imperial colonization, Cadia was the home of a lost fragment of humanity that worshipped the four Gods of Chaos. This society was encountered by the Word Bearers Legion forty years before the Horus Heresy (...). It was on Cadia that the Word Bearers' Primarch, Lorgar, first met Ingethel the Chosen and became inducted into the service of the Foul Powers. This civilization was eventually wiped out by Cyclonic torpedoes.
N'Kari, Bubonicus and Doombreed
In the ancient lore (2nd edition), there were in the Chaos Codex a quatuor of Daemon Princes that were overpowered. Two of them was N'Kari and Bubonicus:
In Codex: Chaos (2nd Edition), N'Kari is stated as a Daemon Prince of Slaanesh instead of a Keeper of Secrets. He was born on an isolated, backwater world which had been trapped in the centre of a violent warp storm for millennia, incidentally on the same backwater world as the Daemon Prince Bubonicus.
N'Kari is now a Keeper of Secrets, hence a Greater Deamon.
Lothar (now known as Bubonicus) was a mortal Champion of Nurgle, born on a backwards planet which remains cut off from the Imperium by warp storms. Raised to daemonhood, he now rules a daemon world within the Eye of Terror, also named Bubonicus.
During the Horus Heresy, Bubonicus was one of many daemons summoned by Erebus, First Chaplain of the Word Bearers, by a dark ritual conducted during the Battle of Calth
A third of these Daemon Princes is Doombreed
Doombreed was one of the first of Khorne's servants. His True Name was long forgotten, remembered only on a scroll of dried skin, but he was once human, a mighty warlord who led armies which ravaged entire nations on Terra long ago in the Age of Terra around M1/M2.
The fourth Daemon Prince from the Codex was M'Kachen, but I don't know anything about its origin, and is now considered a Lord of Change.
Be'lakor was the first mortal elevated to Daemonhood by Chaos. However, much of his origins are hidden behind legend and rumour. Be'lakor himself does much to hide his true origin and history. But nonetheless legends tell of Be’lakor ruling over mortal empires since the dawn of time, the Daemon Prince conquering a world and subjugating its people, forcing them to worship him as a god.
From Lexicanum i just found the list of Demon Princes and Be'lakor popped into my mind. Im sure that there are many, many others that are non-astartes and non Primarchs
