Arktos was an Arcturan criminal. Princess Pandora described him as the "scourge of the nine worlds", the "silver assassin" and the "death merchant". The Fifth Doctor assumed from these titles that he was "some sort of intergalactic criminal mastermind", while Peri later called him "the galaxy's most dangerous criminal". He piloted an invisible spaceship that was expensive to maintain.
Arktos' invisible spaceship used the crashing ship of Zixlyr as a "shield" to land on Peladon undetected. He worked with Elkin to sabotage a trisilicate mining operation to take the valuable trisilicate for themselves. A bomb was set off, killing all the miners in the site. Elkin tried double-crossing Arktos, but knowing this, Arktos deactivated his weapon and killed him. Before he could escape with his collection of trisilicate, Alpha Centauri apprehended him non-violently. (AUDIO: The Bride of Peladon)