Isn't it obvious? The woman that killed every single person I worked with showed up at my door. It seemed prudent to hide any reason for her to realize that she missed one—Cassius to Fiona about Athena (determinant)
Doctor Cassius Leclemaine is an Atlas scientist in Tales from the Borderlands.
Doctor Cassius Leclemaine was an Atlas scientist who run the Atlas Bio Dome facility that was working on biogenetic experimentation on both plants and animals for military purposes, until Atlas abandoned Pandora, leaving most of the employees behind, including him. He had a cat that he lost to the violence of Pandora. He knew very little about the Gortys Project, because it wasn't his department, only that the Dome was a part of it.
He is the last remaining Atlas employee on Pandora. He knew that Athena was murdering every one of his colleagues, so he went into hiding by staying at the Dome facility that Athena missed to destroy. If Fiona stops Athena from trying to kill him, he will help Vaughn escape from being captured after he attacked Vallory. Even eating drakefruit with him later at an unknown location.
In episode 5, Cassius can be recruited by Fiona for her Vault hunting group, if she stopped Athena from killing him (or not interfere). He makes Gortys use a "fireball" during fight with The Traveler. The group later complains about his smell, while he thinks about starting to work for Rhys to rebuild the Atlas Corporation.
Cassius personality is the kind of a lonely and isolated person. Ever since he lost every member of his family, he has become a lone wolf that mostly keeps mumbling to himself about his past.
Cassius was aware that Athena was murdering all of his colleagues. When he was meeting her for the first time, he was hiding his identity from everyone to insure that he wasn't going to be killed.You lying Atlas scum!—Athena yelling at Cassius
Fiona's relationship with Cassius is quite determinant depending on your choices.Don't kill me!—Cassius first words to Fiona
Rhys relationship with Cassius is quite stable. When he heard that Rhys was in charge of the Atlas corporation, he was more then glad to help him with the rebuildment.I have heard a rumor that you are in charge of Atlas now.—Cassius to Rhys (determinant)
If Fiona keeps silence about what do with Cassius and Athena, it will count with the cinematic as she was agree to kill him except that Fiona don't say nothing in that cinematic, but in episode 4 and 5, the silence choice it would count as Fiona had stopped Athena from killing Cassius.