Azkaban

Azkaban is the wizarding prison in J.K. Rowling's Harry Potter series. It is located on a tiny island in the North Sea.

Prisoners in Azkaban were guarded by Dementors, creatures that feed on positive emotions. This means that prisoners eventually lose all hope and good feelings and thoughts. They are forced by the Dementors to relive the darkest, most terrible experiences of their lives over and over again. Most prisoners of Askaban are driven mad, while others just die of despair.

During Voldemort's return to power, the Dementors allowed the escape of a large number of Death Eaters, Voldemort's minions. They eventually deserted Askaban and joined Voldemort, leaving the prison guardless. After Voldemort's defeat, new Minister of Magic Kingsley Shacklebolt made sure that Dementors would have no part in guarding Azkaban. While this caused the place to become a bit more cheerful, it probably prevented a number of problems as well.

Notable Prisoners
Black, Sirius was sent to Azkaban without trial for the betrayal of Lily and James Potter to Voldemort and for killing Peter Pettegrew. Both of these charges were later proved false.

Crouch, Jr. Bartemius "Barty" was sent to Azkaban for participating in the torture of Frank and Alice Longbottom. He escaped disguised as his mother, who died in his place a year later and was buried under his name.

Dumbledore, Percival was sent to Azkaban for attacking three Muggle children after their attack on his daughter.

Hagrid, Rubeus was sent to Azkaban without trial for setting a basilisk on students at Hogwarts. He was proven innocent and set free a few weeks later.

Lestrange, Bellatrix was a Death Eater sent to Azkaban for participating in the torture of the Longbottoms. She later escaped in the mass breakout.

Malfoy, Lucius was a Death Eater captured at the battle at the Department of Mysteries. He later escaped in the mass breakout.

Umbridge, Dolores was sent to Azkaban for crimes against Muggleborns.