He is one of the secondary antagonist of Star Wars: The Old Republic - Shadow of Revan, appearing as one of the primary antagonists of it's Prelude (alongside Colonel Darok).
Darth Arkous's past always was mysterious, even for his closest allies. A veteran in the Galactic War, he became Head of the Military Offence following Darth Arho's death. Secretly, he was also a member of the Order of Revan, a forbidden cult inside the empire.
Darth Arkous summoned an Imperial strike team to assist in the Empire's assault on Tython. Officially, he claimed it'd be a crippling blow against the Republic and the Jedi. Unofficially, he dispatched Lord Goh to recover Rakata technology hidden within the Jedi Temple. The attack on Tython was to coincide with Colonel Rian Darok's attack on Korriban, which also hid Rakata technology. When the Empire received word of the attack, Arkous sent the strike team to retake Korriban to keep up appearances, while at the same time, the Republic retook Tython. Arkous attempted to reestablish contact with Goh only to learn that a Republic strike team had killed him.
Arkous later rendezvoused with Darok on Manaan. Together, they journeyed to an underwater base to meet with a Selkath geneticist named Gorima, to find a way to graft the Rakata technology onto test subjects to create invincible super soldiers for the Order of Revan. However, Arkous' former assistant Lana Beniko, having collaborated with SIS agent Theron Shan, sent a strike team after them. When they confronted Gorima, Arkous and Darok were watching from an observation room. With Gorima's experiments having successfully made the grafting procedure non-lethal, the two conspirators made their escape, leaving a depth charge to destroy the facility and send their enemies to their deaths, unaware that they managed to escape also.
Arkous later sent a coded message to Lana, explaining that he was planning on recruiting her to the Revanites, but his plans changed when she met her new allies. He warned her not to interfere with his plan, cryptically stating that the Revanites are everywhere. Lana and Shan tracked Arkous and Darok to Rakata Prime, the former capital of the Rakatan Infinite Empire, where the Revanites had salvaged fragments of the destroyed Star Forge for Gorima to advance his experiments in the building of an "Infinite Army".
The Republic and Imperial pursuers, joined by the vengeful Wookiee smuggler Jakarro and his protocol droid "partner" C2-D4, confronted Arkous and Darok on the roof of the Temple of the Ancients, and killed them, despite Shan's hopes that they are taken alive for questioning. However, it soon became clear that neither Arkous nor Darok were the leader of the Revanites, but followers of the true master of the Order of Revan; who was soon revealed to be Revan himself.
Lana Beniko was later declared a traitor to the Empire and charged with murdering Arkous, a fact she could not deny due to the influence of the Revanites and was forced to go underground with Shan and Jakarro.
Arkous was shown to be very manipulative and cunning, tricking and manipulating the Dark Council and the Empire into doing acts that would secretly aid the Revanites in their plans. He was also charismatic, and was deceptively kind and praising toward his allies in order to hide his true nature from them.
Skills and Abilities
Arkous was a powerful wielder of the Dark Side and a skilled duelist and was capable of taking on multiple opponents at once alongside Darok. He was also skilled in manipulation and deception and fooled the entire Dark Council to think he was a loyal member of the Empire even in death.