Melek Khoura
Brief:
Melek Khoura is a Daemon Prince, blessed by each of the Great Four, and formerly a Dark Apostle of the Word Bearers Legion, whose sign his warships bear. Known to have access to Federation-grade technology, his threat level is very high. Based on Mr. Cheng's information and the fate of Ms. Lin, he may have some role in the ultimate fate of the Apoidea, a light carrier which did not arrive at Marienne III.

His body possesses two heads, which seem to operate semi-autonomously. One resembles a crow, the other that of a mythical dragon. The former was last seen to be rotten, and the latter oddly-well groomed. It is assumed that these are all manifestations of Chaos' paradoxical nature. Based on his partial affiliation with Tzeentch, he may possess some degree of shapeshifting ability.

He further possesses four arms, but otherwise has fairly conventional form for a Daemon Prince. Analysts note that his limbs number eight in total, matching the number of points on the most widespread symbol of Chaos.

Further information about his background - and true capabilities - is unknown to the Federation at present time.

Name:
Melek Khoura(?) - Word Bearers often shed their old name for another. Since his known name has the same structure as is common among them, it can be assumed that his birth-name is another.

Genotype:
Daemon - presumably once Astartes (geneseed: Lorgar?), and human at birth.

Position:
Daemon Prince

Est. Attributes:
Psi: ~9 (Alpha Plus)
Administration: ?
Combat Potential: ~9 (Extreme)
Warfare: >=5 (Exceptional)
Intelligence: ~8-10 (Extreme)
Charisma: ~8-10 (Extreme)

Known Assets:
Flagship Dreadnought - Est. >1000 Combat Power (Insane)
the "Devourer" or "Dread Pilgrim"
A hulking dreadnought apparently formed from disparate parts. Whether it is a true daemonship is unknown at this time, though it possesses many characteristic traits of such. Though clumsy and somewhat slow in real space-time maneuvering, its raw combat power seems to exceed even that of Belisarius. It apparently incorporates Federation technology into its design.

(Speculative) Word Bearers Host
While hard data is difficult to acquire, as a former Word Bearer who later transformed into a Daemon Prince, it can be assumed that he has at the very least several hundred Astartes and thousands of times that in cultists under his command, and potentially far more.
His ships seem to incorporate Federation technology, but with the notable exception of his flagship, do not seem to exceed ours in performance.

(Speculative) Other
It can be assumed that a Daemon Prince of such extensive means possesses a great deal of other assets. No specific details are known at this time.