Cronan

 was a scientist and a criminal.

He made illegal drugs in an isolated area of Thor Orbital Facility. Amongst those he produced were rush, spectrox and PCM. He also had obtained the means to create vraxoin synthetically. The Sixth Doctor exposed him and he went on the run. He tried to kill the Doctor later, but was tricked into killing himself by Sha'ol. (PROSE: Mission: Impractical)