Cusack

is a member of the Demon Clan. He is Zeldris former master.

Personality
Cusack is very confident in his abilities, requesting Zeldris' permission to exterminate the Seven Deadly Sins, former Fairy King Gloxinia, and former Giant King Drole.

Current arc
After Zeldris claims that he is the most worthy to be the next Demon King, Cusack, along with Chandler, walks into the scene. Cusack says that he can see Zeldris on the throne of the Demon King, and he wants to help him by offering his strength. He then bows down and explains why it took long for them to get out of the seal. He apologizes for eavesdropping Zeldris' conversation with the Demon King, and requests Zeldris' permission to exterminate the Seven Deadly Sins, Gloxinia, and Drole. Zeldris tells him to stand and says that Cusack and Chandler will fill the void of the other nine Commandments. He replies that he is not worthy of his praise. Chandler tells how jealous he is that Zeldris and Cusack have an student-master reunion. Cusack tells him not to worry because they get to serve the demon army again, and reveals that he is Zeldris' former master and Chandler is Meliodas'.

Abilities and Equipment
As Zeldris' former master, Cusack is an extremely powerful demon. Zeldris states that along with Chandler, he is more than enough to fill the nine vacant spots of the legendary Ten Commandments.

Zeldris
Cusack strives to impress Zeldris in any sort of way and admires him calling him the most worthy of being the Demon King. He is also envious when Zeldris praises someone else as he said that if his love for Zeldris was on the line then he would not lose to anyone.

Estarossa
Cusack does not get along with Estarossa as he is quite weary of his actions. He does not understand him or his feeling and action but deduces that there is something out of place from him. However he does acknowledges his strength as he believes his power exceeds even Zeldris.

Chandler
Cusack seems to get along well with Chandler as they talk and walk casually together. We do not know their history but it seems they have a mutual relationship. However Cusack does seem to get annoyed at Chandler when ever Meliodas is mentioned as it upsets the latter as becomes a cry baby and obesses over Meliodas.

Meliodas
We know nothing about their history or relationship, however he does not forgive Meliodas for betraying the Demon Clan. He even calls the Demon King "Far too compassionate".