For generations Dathomir was the home of the Nightsisters, the Force-sensitive witches that ruled the planet. In addition to being able to use the Force, Dathomir had its own unique brand of magick, which emanated from and was strongest on Dathomir itself.
Dathomir was ruled by the Nightsisters, who governed the planet through a matriarchal society. The Nightbrothers, the Zabrak males on the planet, were subservient to them.
During the Clone Wars, Dathomir would come under attack multiple times due to the machinations of Mother Talzin (Darth Maul and Savage Opress' mother) and her rival Darth Sidious, leading to the destruction of most of the inhabitants and settlements on the planet by the Confederacy of Independent Systems after conquering it. Asajj Ventress, a Nightsister trained by Count Dooku, returned to Mother Talzin after her master betrayed her, drawing Dathomir to Dooku's attention and concluding in a battle where all the Nightsisters but Ventress and Mother Talzin were killed.
After, Talzin would be reunited with her two sons Opress and Maul, restoring both the legs and the sanity of the latter before they set off to attack and conquer the galaxy. Through the machinations of Darth Sidious and Count Dooku, Savage Opress and most if not all of the Nightbrothers were killed as was Talzin. Maul's plans were thwarted, leaving him broken and forced into hiding.
Dathomir also came to be Asajj Ventress' resting place after she sacrificed herself to save Quinlan Vos, her love interest, from Count Dooku. As Quinlan and Obi-Wan Kenobi laid her to rest in the waters of Dathomir, a green mist appeared; the spirits of the Nightsisters welcomed Ventress home.
In the days of the Galactic Empire, Maul would return to Dathomir once again, as he and Jedi apprentice Ezra Bridger had become mentally linked by merging two Holocrons together and needed to use Nightsister magick to sever the connection and uncover the information from the Holocrons still locked inside their minds. After, the spirits of the Nightsisters appeared, demanding payment in flesh and blood for use of their magick, then possessed Kanan Jarrus and Sabine Wren, who had followed them. While Maul escaped to chase Obi-Wan Kenobi, whom he had seen in his visions, Ezra fought and destroyed the Nightsister spirits by destroying the altar from which they drew their power and they were bound to.