Who is Zagred and What He has Done
Zagred is a devil (or demon depending on your localization) that acts as the overarching antagonist of the first major saga of Black Clover, an ongoing manga/anime series. Some of his origin remains unknown but what is given is that he is a high ranking member of the devil race, a race known for their ancient, but frightful magic and are capable of possessing humans and granting them a small access of their power. Zagred in particular is a very important character to the story because he is revealed to be the mastermind behind the massacre of the elf tribe, which took place on Licht and Tetia's wedding, an event that was meant to unite the two races together as allies. All of this lead to the series main plot in regards to the Clover Kingdom's major conflicts with the Eye of Midnight Sun, lead by Patolli.
Zagred possessed and manipulated the humans into destroying the elf tribe by using a magic item built by the Wizard King, Lemiel and his assistant, Secré, to take away their magic (of course without their consent and knowing at that). This then lead to many innocent lives being slaughtered in a genocide, including Tetia, the Wizard King's sister and her unborn son from Licht. Licht was then forced to transform himself into a monster that wrecked havoc on the city, as a means to prevent Zagred from taking his body. This forced the Lemiel to destroy someone that was essentially his best friend. This event has lead major emotional scars on different characters, with Patolli, Vetto and Fana growing a deep hatred for humans and swearing to have their revenge on them.
When Zagred revealed all of this to one of Licht's friends and follows, Patolli, it mentally broke him apart because Patolli believed he was carrying on Licht's will and honoring his goal on destroying the humans, when in reality, it made him see the brutal truth that he was just a pawn in Zagred's game and he was betraying Licht's will in wanting to protect the humans. Zagred simply laughed in amusement as he watched Patolli scream in horror. He then takes Licht's grimoire from him and proceeds to corrupt it, then transforms Patolli into a dark elf, a being full of hatred and desires to kill.
So why does he do all of this? Simply because he desires to gain a physical body for him to have access of the living world, so that he can lay waste and chaos on the world around him, using a five-leaf clover grimoire made from the despair he caused on that day.
Black Clover, like many manga stories these days, follows a shonen format, similar to other kinds such as My Hero Academia, Naruto, and Bleach. It starts off gradually light hearted as a means of getting to introduce the characters and setting to their audience and often has comedic moments to balance out the overall tone of the series. But as mentioned previously, a major reoccurring plot element of the story is the events of the massacre on the elf tribe, as the story's main villains are tied to these events. Certain bits are continously added as the story progresses, revealing more and more about the events, which does begin to drive the story to its more serious story telling before it reaches to the climatic point where Zagred is revealed to be the true mastermind behind it all.
Pretty much none, whatsoever. Like many devils and demons that you may find yourself come across in fiction, he is written to be diabolical, cruel and unforgiving, who desires nothing more than what is essentially chaos.
The only argument that could be made here is that he is a devil/demon and by default, his nature is to be chaotic evil. But the thing is that the story doesn't state nor make it clear that Zagred is forcefully bound to do evil things nor does he suffer from moral agencies. He has shown to be very sadistic, taking great delight in making both the human and elf races suffer through their own conflicts and well as his own torturing methods. He sees the whole thing as nothing but a game and that the humans and elves are his playthings that have played their roles in order for his plan to work.
Not only that, but the devils all have different motives and approaches to their goals. Asta's devil for example appears to have motives that are left unexplained for the time being but he has provided his power on numerous occasions for him to win his battle and hasn't made much of an effort of fully gaining control of his body. Megicula is also another devil that has taken over a host named Vanica Zogratis, but she has no interest in laying destruction upon the world. Rather, she is curious about humans and is more invested in performing experiments on them and their magic as she finds them to be a race full of surprises (though of course said experiments are viciously cruel), while Lucifero cooperates with its host, Dante Zogratis in expanding the Spade Kingdom across other kingdoms.
So based on all of this, it is clear that Zagred operates on his own clear terms and thus understands fully of his actions, he just takes great delight in making people suffer. Also, I should point out that Zagred did this with very little resources. All it took was possessing a royal minister and some manipulation for him to get this far.