Metebelis III was a famous blue planet in the Acteon Galaxy. The Third Doctor attempted to travel to Metebelis III multiple times during his tenure as UNIT's scientific advisor on 20th century Earth, describing its unparalleled beauty. When he finally arrived there, he was met by some of the dangerous native wildlife. His interaction with radioactive material there later triggered his regeneration.
The blue moon of Metebelis III gave the whole planet a blue tint at night. It had many different habitats, including desert plains, green forests and mountain ranges. Native species included a giant snake, a species of giant bird and an intelligent, if primitive, species. (TV: The Green Death) It was later colonised by humans. (TV: Planet of the Spiders)
The blue crystals of Metebelis III could break hypnotic spells and mind control. The Doctor used the crystal to break the hypnosis of the computer called BOSS. (TV: The Green Death) They could also enhance intelligence and psychic powers. Another type of stone on the planet could counteract the energy produced by the blue crystals. (TV: Planet of the Spiders)
The Third Doctor attempted to visit Metebelis III a number of times, including once with Jo Grant, on his first trip with the TARDIS after his exile was lifted.
He later visited the world at an unknown time period, when he deliberately wired the TARDIS coordinate programmer to go to the planet, stole a crystal and was attacked by wildlife (TV: The Green Death) including blue birds, venomous blue flowers, and blue unicorns. (TV: Doctor Who and the Green Death)
At some time in the planet's far future, a human starship crash landed there. Humans and sheep survived the trip, as did some spiders. Over the next 433 years, the crystals mutated the spiders into larger, sentient creatures that called themselves the Eight Legs. They enslaved the humans, harvesting and devouring them like livestock; disliking their Earth origins, they decreed the word "spider" forbidden.
The Eight Legs planned to take over the rest of the universe, but required all of the blue crystals. The Doctor's theft of one of the crystals caused the ruler of the Eight Legs, the Great One, to send her minions to Earth to retrieve it. The series of events which followed led to the replacement of the crystal, which flooded the body of the Doctor and the Great One with radiation. This caused the death of the Great One and the regeneration of the Doctor into his fourth incarnation. (TV: Planet of the Spiders)
According to one account, Iris Wildthyme encountered the Eight Legs on the planet with her companion Timmy. Wildthyme habitually claimed the Doctor's adventures as her own, although she claimed the Doctor had copied them from her, rather than the other way around. (PROSE: The Scarlet Empress)
The Sixth Doctor and Jason once visited Metebelis III, which was nowhere near as peaceful as the Doctor had been led Jason to believe. Jason later warned Crystal that she was never to allow the Doctor to take her to the planet. (AUDIO: Beyond the Ultimate Adventure)
Feeling slightly depressed, the Seventh Doctor revisited Metebelis III to try to revive his spirits, hoping the beauty of the planet would give him something to appreciate and the danger would revive his interest in life. This goal was almost too successful when he was captured and nearly eaten by one of the surviving Eight Legs, but he was saved by his next incarnation as he paid a brief visit to his previous self. The Eighth Doctor used the Tissue Compression Eliminator he had recently stolen from the Master to kill the Eight Legs before it could eat them both. (PROSE: The Eight Doctors)
During their intergalactic pub crawl, the Eleventh Doctor, Strax, and Rory Williams visited the Blue Moon Tavern on Metebelis III and drank Lotus Gloom. Rory was shocked to discover that the drink was not consumed through the mouth, but by standing in a bowl of the drink. (COMIC: Time Gentlemen, Please!)
During an encounter with Faction Paradox, the Doctor's history was changed so the Third Doctor regenerated on the planet Dust instead, which also saw him being infected with a Paradox biodata virus. The Eighth Doctor eventually learned the truth about the Faction's interference thanks to the interference of the TARDIS, allowing him to restore his original history and ensure the circumstances of his third incarnation's death occurred on Metebelis III. Before history was restored, the Doctor's TARDIS, corrupted into the Edifice as it attempted to contain the infection in itself to protect the Doctor, also manifested bone spiders as remnants of the timeline it was trying to restore, as well as the temporal "ghost" of the Third Doctor who should have existed before history was changed. (PROSE: Interference - Book One, Interference - Book Two, The Ancestor Cell)
The Eleventh Doctor used a Metebelis crystal to boost the natural psychic abilities of Emma Grayling, in order to create and sustain a wormhole to a pocket universe and to rescue Hila Tacorien. (TV: Hide)