Star whale (The Beast Below)

A star whale was believed to be the last of its kind.

In the 29th century, Earth faced destruction because of solar flares, and the star whale was drawn to the planet by the screams of humanity's' children in an act of compassion. All the peoples of Earth had escaped in massive nation-ships, but the people of the United Kingdom lacked an engine to get them to safety. Unaware of the Star Whale's volunteering, the humans captured him and built their ship around it, and used electric shocks into the pain center of its brain to compel it to move, torturing it for centuries.

The Star Whale was eventually freed after more than 300 years in space, when Amy Pond realised it was willing to drive the ship of its own volition and the torture was actively detrimental rather than necessary. (TV: The Beast Below)