Chandler

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

Current arc
After Zeldris claims that he is the most worthy to be the next Demon King, Chandler, along with Cusack, comes into the scene. After Zeldris and Cusack's conversation, he tells him of his jealousy because Cusack gets to see his student. It is then revealed by Cusack that Chandler is Meliodas' former master.

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

Meliodas
Chandler seems to love his disciple Meliodas very much. He is constantly obsessing over Meliodas a lot as is seen grovelling at the sight of Meliodas inside Perfect Cube.

Zeldris
We also have not seen any interaction between the two demons apart from Zeldris ordering him to rescue Meliodas.

Cusack
Chandler seems to get along well with Cusack as they talk and walk casually together. We do not know their history but it seems they have a mutual relationship. He does seem envious of Cusack as he had a "touching" reunion with Zeldris in good terms.