Melkor and Sauron

Smart, cruel and very strict. but he knows how to lie well. Initially, when Melkor came to Arda, he took the form of the brightest light. This was due to the fact that he loved and longed to take all the light for himself, but it was impossible. Then Melkor turned to darkness, and when he reappeared, because of the anger and hatred boiling in him, his appearance became dark and frightening: taller than clouds, clothed with ice, crowned with smoke and fire; his gaze withered with heat and pierced with cold.

In the time of Utumno and again, starting from the arrival to Ungoliant, the appearance of Melkor was humanoid, but terrible (not hiding the evil of his soul), while of great stature (the Valar, on special occasions, could enlarge their bodies). During the flight from Aman, Melkor's height decreased due to the waste of his strength.

Staying in Aman, Melkor did not betray his evil and wanted to deceive others with his "repentance". He took on a beautiful appearance and could pass for any other of the Valar. After the conversation with Feanor, Melkor disembodied, and the elves saw him like a dark shadow rushing across the sky.

Smart as Melkor, only more cunning and can always find a common language, but only if he needs something from you.
Up to the Fall of Numenor, he was still beautiful in appearance or could take on a beautiful appearance for the time being. Sauron possessed the ability to change his appearance, becoming a huge wolf, a snake and a vampire bat. In Numenor, he was taller than any of the Numenorians (the tallest were 2 meters tall), and his eyes shone like fire. To many, he seemed wonderful, to many — terrible, and to some — evil[6].

After the Fall of Numenor, Sauron could no longer change his appearance, as he spent too much effort on inclining Numenor to evil. From now on, he became dark and terrifying, with black hands in which fire burned, yellow and fire-shrouded eyes without eyelids, with a vertical pupil. He was taller than a man, but not a giant.[7] Gollum noticed during the interrogation that one finger was missing from Sauron's hand (severed by Isildur along with the Ring). Skills - Sauron was the greatest of the Maiar who served Melkor[2]: the most powerful and terrible of his servants, only slightly inferior to his master in evil[8]. Having become a great master in Aule's retinue, Sauron acquired extensive knowledge about the physical substance of the world, as well as forging and all other types of craftsmanship. He has forever preserved the scientific knowledge he received from Aule. Sauron probably knew more about Ainur's Music than Melkor, whose mind was always busy with his own plans. For magical actions, Sauron used gold (including to create a Single ring), since it was the element of Morgoth in the matter of Arda, where his spiritual power was most strongly dispersed. The creation of a Single Ring was similar to what Melkor did during the war with the Valar, scattering his power into the matter of the whole of Arda, thus making it his "ring". Sauron acted wiser in this, since he, as a weaker Ainu, did not have to expend himself on such a scale