Despite being hundreds of years old, Zeref has the appearance of a young man. He wears high-collared red (black in the anime) and tan robes with gold trim, along with a large, flowing white toga draped around his torso. He has short black hair, dark eyes, and abnormally sharp canines. He also wears a circle-shaped necklace.
When angered, Zeref's irises become red and gain a black ring around the pupil, giving him a much more menacing appearance.
Zeref is said to have been the darkest, most evil Mage in the history of the Magic World, mastering the Black Arts and creating many Demons, some of which still wreak havoc in the present.
In the modern era, Zeref seeks to isolate himself and is very calm, sincere, and conflicted. He wishes to die to atone for all the sins he has committed, and may commit in the future. He shows concern for others when he warns them not to come near him, knowing that they would die if they did. He is also somewhat emotionally fragile, as when he realizes that Natsu is not ready to kill him yet, he breaks down in tears. Zeref often kills with no prior incentive or knowledge.
In spite of all this, Zeref is very vindictive, and will punish those who he believes to be evil. This was shown when he ruthlessly killed Hades, whom he thinks has committed a number of unforgivable sins. As a result of his immortal life, Zeref has developed a misanthropic loathing for humanity and its repeated idiosyncrasies of hatred, evil, and conflict.
At some point in the distant past, stated to be around 400 years ago, Zeref witnessed the deaths of many people. Around this time, he also became cursed, and unintentionally took the lives of all those around him. Zeref was described as having alighted in an ancient land, mastered Black Magic, given birth to tens of thousands of Demons, and thrown the world into chaos. However, according to Mard Geer, Zeref cursed himself for becoming immortal, desiring to die and eventually created the Etherious born to kill him with E.N.D. as his final masterpiece.
Because of this, Zeref was sealed away for centuries. One day, however, he managed to set himself free in spite of the fact that not all the keys to his seal had been amassed. His inner darkness, on the other hand, remained sealed.[18] This was later revealed to be false by Zeref himself, who stated that the "keys to Zeref's Resurrection" were something made up by the cults that worship him, as he asserted that he was never asleep in the first place. As Zeref himself stated, years before the story he learned the value of life and because of that he unfortunately lost the ability to use his Magic the way he used to unless he somehow is to forget the value of life. At some point, Zeref learned of Natsu and realized that the Fire Dragon Slayer could someday kill him. Zeref eventually found himself on the secluded Tenrou Island, hoping to stay completely cut off from humanity.
Ultear Milkovich manipulated the young Jellal Fernandes, making him believe he was possessed by the Dark Mage, all in order to get closer to her goal: collecting the keys to Zeref's seal.
On Tenrou island, Zeref lays peacefully, asleep, on the ground. When night descends, he is attacked by a pack of wolves. Their efforts to kill the Dark Mage are, however, in vain, as he releases a wave of Death Magic, killing not only the wolves, but much of the surrounding ecosystem. Zeref then apologizes and wallows in misery, wishing to meet Natsu soon. Later, Carla has a vision, and sees that Zeref will somehow be involved in the S-Class Mage Promotion Trial.
During the trial, he runs into Elfman and Evergreen and warns them to stay away from him, as his Magic is beginning to run rampant. However, when the wave is released, Natsu arrives and saves his fellow comrades from the deathly black wave. Zeref is then shocked to see Natsu, saying that he has "grown", but Natsu says that he doesn't recognize the Dark Mage. When he tells the Fairy Tail Mages that he has been expecting Natsu's arrival, Natsu misinterprets the statement as a declaration of challenge and rushes towards Zeref, landing a fierce blow to his face.
Zeref is unfazed by the punch and stands up, disappointed that Natsu is not ready to kill him, causing him to shed tears of frustration. Zeref then unintentionally releases another wave of Death Magic, but Natsu's scarf absorbs the blast, saving the lives of everyone present. Zeref then proceeds to make his escape, however, Grimoire Heart is now aware of his presence, and seeks to hunt him down. Zeref then rests next to a tree and claims that the world continues to reject him, before crying once more.
Later, Zeref is stated to be in a "state of slumber". Shortly thereafter, the battle between Fairy Tail and Grimoire Heart begins, causing Zeref to wonder if another war is going to take place.
He then crosses paths with Ultear, and comments how sad it is for Grimoire Heart to have managed to anger him. After Zeref asks Ultear if it is power they want, Ultear claims that she wants his entire existence, but Zeref states that he has no intention of assisting them or having anything to do with those in the current era, and that he doesn't want to witness wars or the death of innocent people. Zeref then tells Ultear to stop the attack and leave the island at once, repeating that he is angry, visibly terrifying her with his power. Rustyrose states to Elfman and Evergreen that when they acquire Zeref the current Magic world will end and a new one will begin, an Ultimate Magic World, where those that don't possess Magic will suffer and die; the other Grimoire Heart members say similar things. Zeref himself, however, is powerless against Ultear in his sleeping state and is defeated by her, being warned to underestimate her, as she is the eldest of the Seven Kin of Purgatory. Ultear then says that they have the key which will awaken him; Zeref begs Ultear to stop, but she ignores him and revels in her victory.[31] As Zeref lies unconscious, Ultear holds onto him tightly, stating that he now belongs to her and that he will become the King of the Ultimate Magic World.