Blackheart is a overly-serious demon who is defined by his ambition. Even with his shattered mind, his goal of taking his father's realm for himself remains the one and only thing keeping him going. Being born from hatred and fear of humanity.

In contrast, Shuma-Gorath is generally a bit more laid-back, even cracking jokes on Blackheart's expense. He is also strangely merciful towards earth, as he finds humans interesting, viewing them as we view ants. He even partakes in some human activities