Baldur's Gate: Descent into Avernus
Based on a pact she made with Thavius Kreeg a century ago, Zariel plans to bring Elturel into the river Styx and turn all of its citizens into devils to fight the war against demons.
She once served as a celestial general in an invasion of Hell but it all went wrong. Asmodeus offered her the change to lead his armies in the Blood War and she took it. A tiny sliver within her, known as the Companion, knows this is fucked and knows that mortals deserve better. The Companion still lives.
Zariel had four generals that served her in her invasion. They included:
Gideon and Harumon stayed loyal through her transference into the Lord of the First. Yael and Jandar did not. Yael fled with Zariel's sword, given to her by Zariel under the influence of the Companion, and buried it in Avernus. Jandar stood up against Gideon and Harumon. Gideon turned him into a vampire and Harumon stuck him to the tree of woe on Harumon's Hill seeking to pull from his mind the location of Zariel's sword.