Sauron is a Maiar. Like Gandalf, he's a kind of angel in the Lord of The Rings universe. But while Gandalf is a servant of Manwe, the favorite of the god Eru Illuvatar (chief god in Tolkien's pantheon), Sauron's master is Morgoth (also called Melkor) who for all intents and purposes is this world's devil. But Morgoth was defeated in the distant past and exiled by Eru. Without his master's power, Sauron has to be underhanded to gain power, like the devious underling he is. Sauron's a liar, which is why the Rings of Power finale needs some explaining.
Warning: Spoilers for The Rings of Power finale incoming.
Though in Rings of Power Galadriel says that Sauron is responsible, Morgoth was the one who made Ungolianth (Shelob's mother) devour the light of the trees of Valinor. But after Morgoth's removal from Middle Earth at the hands of an ancient host of elves, men, dwarves, and the combined might of multiple gods, Sauron is left to accomplish the goals his master could not. Sauron does not have Melkor's sheer power. But he does have cunning, and he knows the power of ambition and corruption.
Who is Sauron in 'The Rings of Power'?
Sauron has multiple forms. The two people are most used to are the imposing one where he wears black armor wielding a massive mace, and a beautiful elven male with white hair and gold-like eyes, also called the deceiver. The Rings of Power is set during the time period leading up to the rings' creation before Sauron's wars tore apart middle-earth.
For some interesting perspective, Sauron was once the servant of the god of smithing before Melkor corrupted him (which explains his obsession with crafting).
Maiar can shapeshift at will. Eru won't strip Sauron of this ability until he causes the sinking of Numenor. Meaning throughout the entire 'Rings of Power' series, Sauron can appear as anyone. And yet, he chooses to appear to Galadriel as a refugee on a raft in the middle of the ocean. Halbrand is Sauron in disguise. It makes a lot of sense for Sauron to keep his enemies close, become trusted by Galadriel, earn a smith license in Numenor and rub elbows with Celebrimbor.
How are 'The Rings of Power' rings made?
Celebrimbor will eventually become the creator of the One Ring, as well as all of the other rings of power Sauron scattered across the kingdoms of Middle Earth. Because Halbrand, aka Sauron, can see in Celebrimbor the ambition to create more and more powerful artifacts. In the end, it's deception and Sauron's own brand of seduction that makes him a threat.
Sauron understands your darker impulses and offers you the things you most desire, but always at a terrible price. If you fall to the temptation of his power, he owns you.
This is why Sauron wants to set Galadriel up as a dark queen, in one swoop destroying an enemy and gaining a powerful servant. It's totally possible she'd succumb as well, Galadriel herself owns up to her temptations in 'The Fellowship of the Ring' when Frodo offers the One Ring to her. "In place of a dark lord you would have a queen, not dark but beautiful and terrible as the dawn! Treacherous as the sea! Stronger than the foundations of the earth!"