Darth Jadus is renowned both within the Empire and by the games playerbase as the smartest and most cunning Sith to have existed in this time period. Shrouded in mystery, Jadus sat on the Dark Council where he operated Imperial Intelligence, giving him way to the Empire’s greatest secrets and classified information.

After his apparent death abord his dreadnaught ‘Dominator’ , his only known apprentice and daughter, Darth Zhorrid was promoted to sit in his place aboard the Dark Council. It would come through fate that his daughter, distraught with the loss of her father, organised Cipher Nine (Agent Story) and Imperial Intelligence to track down the terrorist cell responsible for his death.
Through various means it was discovered by Cipher Nine that Darth Jadus had faked his own death, drawing out his follow Dark Councilors to squabble over the temporary power vacuum left in his absence, allowing him to further his own goals under the mask of death.
When the Empire discovered that he was, infact still alive, Darth Jadus plan was already nearing fruition. He had created a series of doomsday satellites known as “Eradicators” capable of reigning terror upon Dromund Kaas and killing the rest of the Dark Council. Darth Jadus had planned to swoop in the aftermath of the collapsing Sith Empire and found its rebirth as a stronger society devoid of Sith as leaders that caused the Empire’s own failure, until he was stopped by Cipher Nine in person aboard the bridge of the Dominator.

It is up to the player to determine how Cipher Nine deals with Darth Jadus, whatever choice is made: whether you let him go, side with him or incarcerate him for his crimes, he will always escape into the shadows, never to be seen again.

However this is where things get interesting for Darth Jadus, as if Cipher Nine sides with him and lets him escape, he will contact you in the future. As the story continues, he is the only Sith that believes the Star Cabal exists as an entity, giving Intelligence the authority to command Cipher Nine to hunt them. No other companion or story character you attempt to tell of the Star Cabal in the story believes you until Act 3.

Darth Jadus, and even his daughter Zhorrid would then fade into the background of obscurity and lore. By the time of Shadow of Revan, Imperial Intelligence would be reformed into Sith Intelligence as Lana Beniko takes leadership over Darth Zhorrid who hasn’t been seen again.

It would not be until nearly fifteen years after Darth Jadus’ plan was foiled that he would be mentioned again.
During the War on Iokath, Lana Beniko and the Outlander idly chat about suspects causing the upheval of the Alliance and the Republic & Empire skirmishing on Iokath. During this conversation Lana mentions that Darth Jadus has been rumored to still be very well and alive, and has potentially been pulling strings on galactic conflicts once more after the Eternal Empire fell when the Outlander defeated Vaylin.

Sources:

Agent Story Act 1 – Star Wars the Old Republic
Story choice: Agent Story- ‘Hand of Jadus’ side with him aboard the Dominator.
Codex Entry: Darth Jadus – Agent Story only
Codex Entry: Darth Zhorrid – Agent Story only
Iokath Storyline – Knights of the Eternal Throne