Anakin Skywalker, now known as Darth Vader, embarked on a specific task that brought him to the river moon of Al'doleem. This occurred early on during the Great Jedi Purge taking place in 19 BBY.
Vader journeyed to this satellite to find and confront the Jedi, Kirak Infil'a. Darth Sidious, his Sith Master, had instructed him to acquire a kyber crystal from a defeated Jedi in combat. Vader was then to corrupt this crystal for his own use. Infil'a, having distanced himself from the Jedi Order through the Barash Vow, had survived the widespread extermination following Order 66, making him a prime target for Vader to obtain the desired crystal.
During Vader's lightsaber duel with Infil'a, three officers from the Am'balaar City police attempted to intervene, as the battle unfolded on essential city infrastructure. The Sith Lord tried to hurl the officers away, but Infil'a managed to save them. Vader then exploited the Force to demolish other structures, threatening a city-wide flood. Infil'a, aghast, tried to contain the water, but Vader seized the opportunity to seize the Jedi's lightsaber and lift him into the air. As the Jedi was being Force choked, he helplessly witnessed the flood begin. Vader proceeded to execute Infil'a, letting the Jedi's lifeless form plunge into the rising waters.
After securing the crystal, Darth Vader's droid piloted their vessel to Mustafar. Once inside a Sith cave, Vader initiated the process of corrupting the crystal. He rejected a vision where he returned to the light side of the Force and successfully twisted the crystal to his dark will.
The Al'doleem mission was first depicted in Darth Vader: Dark Lord of the Sith 3: Fortress Vader, Part III, a canon comic book from 2017. It was written by Charles Soule and the artwork was created by Giuseppe Camuncoli.