Adar is an elf who was manipulated with evil magic. He served under Morgoth and claims that he killed Sauron. He does not seem to recognize Halbrand as Sauron, and yet he carries out what we can assume is his master's evil bidding by setting in motion the events that burn the Southlands and create Mordor.
Clearly there is a lot of history between these two servants of Morgoth. When Halbrand and Galadriel captured Adar, Adar seemed not to recognize Halbrand as Sauron. Adar also claimed to have killed Sauron after watching Sauron experiment on the orcs, whom Adar sees as his children.
After Morgoth's defeat, Adar at first served Sauron in the latter's mission to discover a way to subdue other forms of life. However, disillusioned by Sauron's cruelty to the Orcs, Adar turned on Morgoth's successor and struck him down, believing for centuries afterward that he had slain Sauron.
Because of his age, Adar would have had a prominent place in Morgoth's army, but he was still subservient to Sauron. So, when Sauron took over, Adar became his servant until Sauron started to experiment on Orcs. Because they were his children, Adar rebelled, and to his knowledge, they killed Sauron.
Adar as the Elf Who Became the First Orc, Created by Morgoth
He is one of the elves Morgoth “tortured” and “twisted” into “a new and ruined form of life.” She called those elves, the first orcs, “the Moriondor, the Sons of the Dark.” But Adar says they prefer another name: Uruk.
Turns out, Adar was one of the first orcs ever created — explaining why the orcs call him "father" in Sindarin. As Galadriel explains, in the First Age, the Dark Lord Morgoth captured and tortured elves, turning them into twisted, ruined creatures that would later become the orcs as we know them.
Adar revealed his entire story to Galadriel, and what he told her will change her mission in the Second Age. Adar is an original Orc, and he served Morgoth and Sauron. His life has been one of darkness, but his attack on the Southlands is a desperate attempt to create a home for his offspring.
Adar soon became disillusioned with the Dark Lord and disgusted by the selfish sacrificing of his "children" for dabblings in the Unseen World. Having had enough of slavery, Adar broke his shackles to Sauron and turned on him, going as far as to slay him.
"So I think in his pitch to Galadriel, it cannot mean that he loves her or that there's any kind of romantic relationship. There should be no ambiguity around the fact that Sauron is evil — he's terrible, and he's using Galadriel to enhance his power."
Because of these future events in Middle-earth's plot concerning Sauron, it's far more likely that Adar never attacked Sauron, but he's lying to Galadriel about doing so to keep his current location and identity secret.
There have been consistent reports he is a fallen Elf, a quite dramatic departure from Tolkien's own lore given he moved away from the idea that Elves can fall to the Shadow.
So, Halbrand would hold a grudge if he is Sauron and Adar had tried to kill him (and perhaps severely injured him), but now Sauron has taken the form of Halbrand, then Adar would not recognise him.
Halbrand does not deny his heroism out of bashful humility, though; he knows that as Sauron, he's not the hero she wants him to be for the Southlands -- not when his plans involve scorching it into Mordor. No, Halbrand was never a hero, nor did he ever claim to be.
Elrond discovered the scroll that revealed that Halbrand couldn't be King of the Southlanders, so it's likely that he realized that Halbrand was Sauron and that he escaped. Knowing that Sauron is on the loose, he could warn the dwarves of the growing evil and encourage them to forge their own rings.
As for whether Halbrand actually loved or romantically desired Galadriel is to be determined. Sauron is an expert manipulator and likely sees Galadriel and her power as an asset. In line with the old adage, "Keep your friends close; keep your enemies closer," he'd rather have her on his side than against him.
In his notes, Tolkien remarks that Sauron saw Galadriel as his equal. Add that to the fact that she's untrusting of Sauron (yes, even when he's in his Annatar guise) and an unwavering, single-minded force, and it's more likely than not that Sauron feared Galadriel — or the potential she held to upend his plans.
Plus, he makes the compelling argument that while he lusts for power, she has a good heart and would help him remain good rather than turning to evil. But when it becomes clear to Galadriel that Halbrand/Sauron cannot tell the difference between “saving” and “ruling” Middle-earth, she rejects his proposal.
Galadriel was one of the Ñoldor who came to Middle-earth wishing to see the lands and rule a realm of her own. She came with the second host of Elves from Aman with Fingolfin and Finrod. In Doriath, she and Celeborn fell in love and married.
Adar, therefore, seems to honestly believe he killed the Dark Lord. He's almost certainly mistaken. Sauron is one of the Maiar - angelic and immortal spirits from the beginning of time. Since the Maiar are divine, primordial beings, they don't die in the traditional sense.
It revealed Adar no longer serves Sauron, as we initially thought the mutilated elf might. Throughout The Rings of Power, we've slowly uncovered Adar's true identity. The show has offered us insight into the one-time elf, his origins, and why the otherwise hateful orcs adore Adar as they do.
When Galadriel calls Adar's kind — captured Elves tortured and twisted into becoming Morgoth's evil minions — “Moriondor,” which translates to “sons of the dark” in Elvish, Adar says he prefers the term “Uruk,” which is the word for “Orc” in the Black Speech of Mordor.
According to Galadriel, when the Elves first awoke at the beginning of the First Age, Adar was possibly one of many of them who were taken by Morgoth. He was tortured and twisted, becoming one of the first Orcs, a new and ruinous form of life.
Saving Galadriel at sea was likely a method of gaining her trust, since Sauron would need an Elf's friendship to enter their realm. Whether he targeted Galadriel specifically because he could exploit her bloody-minded rage and broken heart is unclear.
