Cecil Stedman, a key character in Invincible Season 3 is the director of the Global Defense Agency (GDA). He is a government operative tasked with protecting Earth from superpowered threats. He is shown often using ruthless tactics to achieve his goals which at times puts him against the protagonist. Therefore, being a strong character in the show, fans are speculating about the possibility of Cecil becoming a full-fledged villain in Invincible Season 3. There are strong hints that his morally gray decisions may push him further into an antagonistic role.
Let's dive deeper.
Cecil's character and the speculations around him being a villain in Invincible season 3, explored
In Season 3, the second episode offers some perspective on the character's past and the reason why he is harsh on heroes. It opens with Cecil receiving a tip for a criminal activity that sets him up on a mission alone. The character is shown always giving a chance to the baddies to reform and is willing to sacrifice himself for the sake of humanity. But what makes him different from the protagonist is his approach to achieving what he wants to achieve.
In seasons 1 and 2, Cecil is shown as evidently manipulative and makes morally questionable decisions to protect Earth from threats like Omni-Man and the Viltrumites. However, the character comes with its own edge and complexities. He genuinely believes in saving Earth despite his methods being wrong.
The incident in which Cecil bears the burn of the gas quite literally to save the lives of other people reveals Cecil's cold and tactical mindset. This incident scarred him with pale ghostlike skin.
The one-liner of the episode "A Deal with the Devil" says "Sometimes, to protect the world, you have to make a deal with the devil, even if it means sacrificing your soul." This perfectly encapsulates the moral dilemma faced by Cecil Stedman and the Global Defense Agency (GDA).
Cecil and his conflict with Invincible Season 3 protagonist Mark

Though it can be assumed that Cecil is not outrightly an evil villain in Season 3, he can be considered an antagonist keeping in light the conflict he has with Mark. The clash between the two characters is because of their different approaches despite having a common goal.
Cecil even implants a device on Mark that can sometimes weaken him and reduce his powers. He further hires D.A. Sinclair and Darkwing II to work for him despite knowing their wrongdoings. This compels Mark to part ways with Cecil.
When Mark tells the team of Guardians of the Globe about what Cecil did to him, the team scatters with Rex Splode, Shrinking Rae, Monster Girl, Robot/Rudy, and Bulletproof, leaving the team.
As Invincible continues, the tension between idealism (Mark) and realism (Cecil) will likely deepen. While Mark strives to be the "good guy," Cecil will continue making ruthless but calculated decisions to safeguard Earth.