Overlord presents a complex world, shifting around what's considered right and wrong, with Ainz Ooal Gown standing right in the middle of it all. As the supreme leader of the Great Tomb of Nazarick, much intrigue and conflict in the story is driven by the actions of Ainz. His unimaginable power and strategic mind serve him well, but his actual intentions often prove a bit too hard to crack.
Fans find themselves wondering whether Ainz is a hero of the new world or a villain who would do anything to dominate. The debate about Ainz's true nature remains central to understanding the dynamics of the story.
Ainz Ooal Gown or Momonga is technically known as an anti-hero with villainous tendencies and is focused on achieving his goals regardless of the consequences.
Disclaimer: This article reflects the writer's opinion and includes spoilers.
Is Ainz Ooal Gown from Overlord a villain?

Ainz Ooal Gown from Overlord is an anti-hero, not a straightforward villain. Even though his actions point more toward cruelty and domination, his motivation is way more complex than that of a typical villain.
Ainz does not commit evil for the sake of harming someone, instead, he does so because of his loyalty to Nazarick, and because he wants to protect it and find an explanation for this new world that has brought him into existence.
It is his ruthless decision-making that makes Ainz seem villainous. He kills many of those opposing him and manipulates people to expand his influence. However, these choices largely reflect his strategic thinking as a leader, in an attempt to secure power for and safeguard the legacy of his guild.
His attitude toward most humans resonates with how he was once a human player who transformed into this undead creature, after which he continued to alter his outlook on what is right or wrong and even life in general.
Despite this, Ainz doesn't reach out for destruction or chaos without reason. In fact, sometimes he'll look back upon things he's done and wonder if it's been too much which shows a level of internal conflict typical of an anti-hero. His subordinates view him as a near-omnipotent ruler, and Ainz, playing off this, makes decisions that bring them benefit, even if this means horridly brutal results.
How Ainz Ooal Gown's character develops in Overlord, explained

Ainz Ooal Gown's character in the series Overlord grows from a conservative leader unfamiliar with his position to an expert ruler embracing his power. Initially, after being transported to the new world he was cautious about what the NPCs he had considered just mere game constructs would do.
As the story unfolds, so does the character. He becomes the expected candidate for the supreme ruler of Nazarick. His strategic decisions are paired now with calm authority to establish loyalty.
He grows in terms of his perception of the new world. As he becomes familiar with the political landscapes, it increases his confidence, and from being reactive, he expands his reach through proactive action. His relationship with his subordinates also changes. What begins as tactical leadership becomes an affair of absolute faith and respect.
On the emotional scale, Ainz states that being in an undead state restricts the feeling of power in emotions. This aspect took away part of the sensitivity towards his previous human form and influenced how he reacted to doing things in a moral and meaningful way versus simply doing things for his own purposes within Nazarick.
Final thoughts

Ainz Ooal Gown, also known as Momonga, is not a straightforward villain in Overlord but an anti-hero with complicated motivations. Being cruel and manipulative, his motives are intricately woven with his loyalty to Nazarick as well as his own struggles to find power in a new world.
His calculated decisions make him appear cold-blooded but they are a product of his strategic mind. Ainz's complex story and inner struggle act to define his role as the powerful anti-hero. Much of the drama and suspense in Overlord center around this.