Torajii

Torajii is a sentient star encountered in the Doctor Who episode 42.

Anatomy
Unlike most stars Torajii is a sentient being. Like any other star is composed of a variety of gassess and chemicals. It can control and manipulate these elements to take over other being from a distance. Once its taken a victim over it can control the body like a puppet. Victims of possession are capable or releaseing intense heat from their eyes; enough to vaporize a human body to ashes. Torajii is capable of using the memories of those it has infected to its own advantage and intelligently react to problems

Forcibly removing a piece of Torajii will cause it incredible pain. The Doctor while under possession described the pain to be akin to having ones heart pulled out.

History
Torajii was first encountered as a sentient being when the crew of the SS Pentallian performed an illegal Fusion Scope; removing gassess from the star to power the ship. The pain of the "assault" drove Torajii into a maddened rage where it sought to take vengeance on the ship and reclaim its missing parts.

Gas from the star travelled to the ship and infected several crewmen; transforming them into its agents who would kill the non infected and crash the ship into the sun.

When the Doctor attempted to rescue Martha and another crewman from a pod that had been jettisoned he to was infected.