Keiko the whale from "Free Willy" was put into an unhealthy, small pool in Mexico City where he was malnourished after achieving fame from the movie.
Keiko was the first captive orca to ever be returned to life in the ocean, and he died back in 2003. His death was unexpected because he was in good health, but the day before his death he was lethargic and fatigued. He swam to a shore on December 12th, 2003, and died. He died of pneumonia.
He was captured in 1979 and sold to Mexico City where he performed for crowds. He eventually starred in Free Willy, and after much debate was set free like his character. Before that, though, he was put back in the Mexico City pool while his fate was decided. It’s thought that how he was treated then played into his death later, because of how malnourished and sickly he became there.