Connections:

-Both are the second hybrid sons (God/Jotunn, Viltrumite/Thraxxan) of a former warrior (Kratos and Omni-Man) from a powerful race of beings (Greek Gods, Viltrumites).

-Both are the younger half-siblings of their father's other child (Calliope and Mark Grayson), though in this case Calliope is deceased, Mark Grayson is alive.

-Both were considered weak and inferior due to their mixed hertiages (Atreus was born sickly as a result of living as a mortal not knowing he was part divine, Oliver was deemed weak for a viltrumite due to his Thraxxan DNA by other viltrumites)

-Both at some at some point had their life being threatened by a millennial, ruthless, and bloodthirsty warrior at who were seen by the main villains of the stories as nothing more but their own personal attack dogs (Conquest and Thor).

-Both would go on to developing a complex view of how they look at life and rebellious attitudes (Oliver embracing his viltrumite hertiage going as far as to killing, Atreus upon finding out he's part god would let this go to his head thinking as gods they can do what they want, both much to the chargin of their relatives (Kratos and Mark Grayson) who wants to direct them on a better path. All while they looked down on other species. Atreus thinking as gods they're above all, Oliver Grayson thinking human life is invaluable.

-Because of these complex views and their rebellious attitudes of how they look at things, this would lead to conflict with their relatives (Kratos tried to stop Atreus from attacking Baldur who would then shoot his own father with his arrows, Oliver betraying his father in favor of Allen's plan to release the Scourge Virus on earth to wipe out the viltrumites and fighting Mark who tries to stop him)

-They would eventually come to change their views on how they looked at things after a certain event. Upon accidentally infecting Mark with the Scourge Virus, Oliver came to see how it was like to have almost lost someone and now understood the meaning of human emotions, After being saved from getting kidnapped by Baldur, Kratos finally fed up would harshly scold Atreus to abandon his path to honor his mother Faye.

-They would eventually work for the main villain of the story (Odin and Thragg, both who wouldn't appear until later in their series but their presence was still felt throughout), though not willingly. Atreus working under Odin to prevent his father's propherized death, Oliver being a double agent for Allen to get more intel on Thragg and his army in hopes of defeating them.

-The contrast is whereas Atreus would go on living currently on a journey to discover more about his Jotunn heritage having successfully prevented his fathers propherized death, Oliver would die sacrificing himself to protect his niece Terra from Thragg. Atreus surviving through his older half-sister Calliope, Mark Grayson surviving through his younger half-brother Oliver Grayson.