Mephistopheles Arkadian

Mephistopheles Arkadian was a human intergalactic arms dealer who also dealt in temporal artefacts. He was in league with the Free Time movement, but stayed impartial. Leela, K9 Mark I and Commander Torvald encountered him on Gryben whilst searching for information about the movement and the threat of a Timonic Fusion Device. He led them to Nepenthe and was himself taken to Gallifrey. He was the first person to hail Lady President Romana II as "Imperiatrix". (AUDIO: Weapon of Choice)

Later, he invited Romana and Leela to the Calais Transcontinental Express while it was travelling through Austria on 3 September 1939 to learn about the fascist sympathiser Cecelia "Sissy" Pollard, (the younger sister of the Eighth Doctor's companion Charley Pollard) and Commander Torvald. (AUDIO: A Blind Eye)

After the fall of the Matrix, Lord President Matthias invited him to remove Pandora's stockpile of weapons. Matthias, however, was in league with Irving Braxiatel, to whom he had sold his Collection. When Braxiatel's plan was completed, Arkadian appropriated a Battle TARDIS with the weapons, but was killed by Elbon, who was affected by the Dogma Virus, during his attempt to flee Gallifrey. (AUDIO: Panacea)

Behind the scenes
The Arcadian representative from the comic story Smart Bombs may have been intended to be Mephistopheles Arkadian.