-Once normal humans before big events drastically changed their physiology, pushing their body beyond human limit and gifting them immortality with both needing to refresh these through consumption of others (Savage drinking his enemies blood and committing cannibalism to regenerate his powers/Kleiss needing to absorb nanites to keep himself stable).
-They are rulers, scientists and cunning leaders, while one could get fooled by their polite behavior and charisma from outside, they are deeply selfish and completely heartless people, being highly manipulative psychopaths with massive god complexes.
-Both are villainous masterminds, garnering big groups of antagonists to their side for their plans to conquer the world and establish a new world order in their vision. Both are very power-hungry and super theatrical geniuses who manipulate everyone around them and further their goals through long game planning skills.
-They have illusions of grandeur and would be heavily involved in politics, even somehow managing make themselves public figures and continue scheming behind their good images for a time. Both show social darwinist beliefs and have a penchant for trying to steal the power of heroes.
-They are rivals with amnesiac protaganists (Resurrection man and Rex Salazar) who gained their powers through experiments involving nanotechnology and have powers that directly parallel their own.
-Both also influenced the history for years hundreds of years in past with both getting involved in time travel bullshit in events wherein there would be a desperate attempt to defeat them throughout specific forces chasing them in the hopes of ending them throughout time (Breach chasing Kleiss for thousands of years in the past and Rip Hunter repeatedly trying to kill Vandal in different periods of his life).
-Kleiss is member of an inhuman race (EVO) that has supremacist beliefs towards it, considering it superior to humans and has a deep hatred for humans whereas Vandal is one of the first humans, being ancestor to a huge majority of human race and either being involved with or straight up being notable figures in history.
-On a more misc side, while Vandal’s appearance changes from time to time, both had similar long flowing black hairs and Kleiss briefly grew a beard that looked similar to Vandal’s at one point. They also have a habit of beefing with children
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