Merlin was first given demonic parentage by Geoffrey of Monmouth. Geoffrey calls Merlin a “fatherless boy” because his mother is a nun who swears that she has never been with any man. ... This something is identified in the narrative as an incubus-demon.

Is Merlin from the Seven Deadly Sins a demon?

Merlin「マーリン」 is the Boar's Sin of Gluttony「 暴食の罪 ボア・シン , Boa Shin」of the Seven Deadly Sins. She is regarded as the greatest mage in Britannia. Her Sacred Treasure is the Morning Star Aldan, a floating orb she can summon at will and often uses in conjunction with her spells and her inherent power Infinity.

What race is Merlin?

Merlin is a human from Belialuin.

Belialuin was described as the "capital of the wizards" 3000 years before the events of Seven Deadly Sins.