Final answer:
Ekrizdis created Azkaban as a private fortress for practicing dark arts and later it was used as a prison guarded by Dementors.
Step-by-step explanation:
Ekrizdis initially created Azkaban to serve as his private fortress and laboratory where he could practice dark magic far from the eyes of the wizarding authorities. In time, Azkaban became synonymous with punishment and captivity as it was repurposed into a prison for witches and wizards who broke the law. Ekrizdis was known for luring, torturing, and killing Muggle sailors on the island, filling the place with dark creatures such as Dementors, which were later used to guard the prison that Azkaban became after Ekrizdis's disappearance and the discovery of the fortress by the Ministry of Magic.