He is voiced by Akira Ishida in the Japanese version of the anime, and by Joel McDonald in the English version of the anime.
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 pendant where he keeps a childhood picture of Natsu and himself.
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, trustworthy, straightforward, optimistic, 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 and vulnerable, 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 antagonistic, so he 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.
After finally died peacefully with Mavis, and Acnologia has been defeated by Natsu, Zeref is now a loving father and a family man in afterlife.