The First Jedi Temple (also known as the Ahch-To Jedi Temple) is a place that first appeared in the 2015 film, Star Wars: The Force Awakens. It is an ancient Jedi Temple located on the planet Ahch-To, established and maintained by the Jedi Order. It was the first of many temples built throughout the galaxy, and one of the few that were not destroyed by the Galactic Empire. Luke Skywalker came to live there after his new generation of Jedi Knights were killed, and his apprentice and nephew Ben Solo turned to the dark side.
Sometime after the Jedi Order was founded, the Jedi built a Jedi Temple on the planet Ahch-To to serve as a Jedi academy to train new generation of Jedi Knights, it was the very first Jedi Temple ever built (apparently) even before the Clone Wars and the Jedi Purge respectively began, the Ahch-To Jedi Temple was abandoned by the Jedi Order.
Sometime after the Jedi massacre, Jedi Master Luke Skywalker seek out the Ahch-To Jedi Temple (prior to his disappearance; Luke gave two pieces of the map to the Ahch-To Jedi Temple's location, one to R2-D2, his astromech droid, and another to Lor San Tekka, a member of the Church of the Force, for unknown reasons) after most of the apprentices were killed when his Jedi Temple was destroyed, Luke eventually found the Ahch-To Jedi Temple, and intended to remain in hiding on Ahch-To until the time of his death, so that the Jedi Order would end with him.