Torajii

Torajii was the sentient star at the center of the Torajii System.

It was first encountered by Humans when a cargo ship, the S.S. Pentallian, hurriedly took some gas from the star as fuel for an illegal fusion scoop. Unaware that they were dealing with a sentient being, the fusion scoop caused Torajii incredible pain and brought it to a maddening rage where it sought to take revenge of the ship and regain what had been stolen from it. Gas from the star travelled to the starship and possessed two members of the crew, who then went on to sabotage the ship and kill many crew members with the intense heat which radiated from their eyes (which meant that they needed to wear welding helmets).

Eventually the gas possessed the Doctor, who told the remainder of the crew the source of the problem and asked them to dump the illegal fuel into the star, which they did, so the star left them alone, allowing them to leave the system to itself.

Despite its actions the Doctor held no hostilities towards Torajii, and sympathised with its plight. He was however angry at Kathryn McDonnell and her crew stating while under the Sun's control that the crew had "scooped out its heart, and now it's screaming" he then chided humanity for taking what they wanted without thought of who they would harm. At the end of the episode the Doctor told the surviving crew to place buoys around Torajii so that no one would attempt to fusion scoop there, stating that as a sentient being Torajii "deserved protection." (DW: 42)

Torajii displayed a high level of intelligence instead of just acting like a wounded animal, as it was able to use the infected crew's knowledge to its own advantage and attack the ship in the most effective way. Also, when it sensed the crew were close to escape it spread the infection, allowing it to attack on two fronts.