Although Darth Vader was instrumental in the Jedi Purge that marked the beginning of the Dark Times for the Star Wars galaxy, he did secretly save the next generation of Jedi from Emperor Palpatine. In the aftermath of Revenge of the Sith, Darth Vader was tasked with hunting down and bringing Jedi Archivist Jocasta Nu before his new Sith master who wanted her alive. However, Darth Vader made a critical decision, one that proved how unbalanced he was in the Force at the onset of his dark side path.

https://screenrant.com/star-wars-darth-vader-saved-next-generation-jedi/