Ernst Frederik Egin is an anime exclusive for the anime adaption of Blue Exorcist. He is portrayed as a man that is more than willing to kill anyone in his way of killing all Demons including his own family without a hint of regret.
It is revealed before the beginning of the series he often sent his followers to kill Demons even if said Demons were peaceful or not harming anyone. At some point his daughter Yuri Egin befriended and became pregnant with Satan's children. Upon hearing of this Ernst demanded Yuri have an abortion and ignored her when she pointed out that Humans and Demons could live in harmony. When Yuri refused to get an abortion Ernst planned and attempted to burn her at the stake so as to prevent the children being born. Satan attempts to save Yuri from her fate but has trouble finding a strong enough host which after a few tries he takes over Ernst who miraculously survives though he does suffer sever burns. Even after his daughter escapes due to Satan's help, Ernst orders his men to hunt Yuri down and kill her and her children. Later when Ernst finds out that both his grandsons lived; Rin and Yukio Okumura and that his daughter died but he shows no sympathy and only keeps them alive to use later.
When he first meet Yukio he tells him he is grandfather and that he needs him and in return he will be able to make both Rin and Yukio fully human by destroying Satan, all Demons and even Gehenna (Hell) with a weapon he has been working on that he calls the Messiah which has taken a minimum of fifteen years to build. Ernst then promotes Yukio to the rank of Paladin to ensure that Rin will cooperate and further his goal of eradicating all Demons once and for all. Eventually they capture Rin and after sacrificing several individuals with the intention of killing Rin to open the Gehenna Gate aka a portal to Gehenna itself. Yukio points out Ernst promised he would only cure Rin and himself not that he'd kill them only for Ernst to merely remark that he lied and Rin will die and be seen as a "hero" in history since he will of helped wipe out all Demons. Yukio offers to take his place which Ernst accepts seeing it as a wonderful idea since Rin's blood might not be enough. When the Gehenna Gate finally opens he brags about his apparent victory and uses the Messiah believing he has finally obtained his lifelong goal.
Unfortunately for Ernst it turns out the Messiah was far too weak to destroy Gehenna or Satan whom now decided to use Yukio as a host since he was the ideal vessel. Ernst falls into the Gehenna Gate and is seeming being pulled into Gehenna, trying to escape he pitifully begs to Yukio to save him. However as Yukio is fighting for control of his body, Satan shows his son his memories and reveals not only what Ernst did but that Satan is trying to fulfill Yin's wish for a world where Demons and Humans can coexist by merging the two worlds. The now Demonically enhanced Yukio grabs Ernst and demands to know why he tried to kill Yin. Ernst quickly confirms what Satan had said by asking how he knew the truth only then to point out he hates all Demons including his own grandchildren saying they shouldn't exist only to then be sucked back into the Gehenna Gate and presumably banished into Gehenna where he will remain for eternity.
Ernst is shown to be a cold, arrogant, and remorseless man who was more than willing to sacrifice his daughter and grandchildren saying it would of been bad of enough no matter who the father was let alone a Demon like Satan. He is portrayed as a genocidal man who hates all Demons feeling they are all evil by default and wants to eradicate them despite it being shown that some Demons are friendly. He will put up a polite and civil especially for his grandsons but it is later revealed he hates said grandsons and doesn't even believe they should exist. Ernst is also shown to be a surreptitious hypocrite as he demands his daughter have an abortion despite the organization he leads believing that it is a sin and should never happen solely to avoid what Ernst believes would be a disgrace/humiliation. Ernst is also shown to be a coward at heart always making others do his dirty work and when he got stuck in the substance that forms the Gehenna Gate, he pathetically begs for help and to be spared by his grandson, Yukio.