Lukas (Regenerators' timeline)

Lukastopherax, commonly known as Lukas, was a Chancellery Guard Commander, as well as aide and bodyguard to President Romana during her third incarnation.

Lukas was once a student at the Time Lord Academy, where he wrote a paper on secret societies.

Romana charged him to follow and monitor Narvin think that he might be betraying her. At the academy, he specialised in research about secret orders on Gallifrey including sects who worshipped Rassilon, Omega and the Other, so could tell Romana about the Adherents of Ohm. There was an assassination attempt on his life but Narvin saved him. He travelled with his president to Omega's domain but had never travelled through time before and found it disorientating. He remained back in Omega's domain to allow Narvin, Ace and Romana to escape. The domain started to collapse around him. (AUDIO: Intervention Earth)

Alternate timeline
A version of Lukas was also encountered on a different Gallifrey from an alternate timeline visited by Romana II, Leela and Narvin before any of them met the Lukas from their own timeline.

He was a Chancellery Guard assigned by Slyne to protect Romana from assassination attempts. (AUDIO: Emancipation) He later took Jonias to see Romana II and Narvin. Lukas suggested that Hector's group were terrorists and wanted to send a squad over to them to stop them from leaving. (AUDIO: Evolution) He helped the Chancellery Guard to reclaim Lord Zakar from the freed slaves who had captured him in order to place him on trial for murder. He tried to stop Science Minister Kavil from entering the Panopticon on urgent business. (AUDIO: Arbitration) When the Daleks invaded Gallifrey, he was ordered to protect Romana and remove her from the Panopticon. Assuming that Slyne was dead, he led her to safety away from the Daleks and later took Romana, Leela and Narvin to the armoury to find some weapons that could defeat the Daleks. He was exterminated by the Daleks when they entered the armoury. (AUDIO: Extermination)

Behind the scenes
Although his full name, Lukastopherax, comes from the Big Finish Productions audio stories Extermination and Intervention Earth, its spelling is pure conjecture.