Genuinely cannot get over how perfect Halbrand as a name is I would like to give the writer who came up with it a huge kiss.
Like, in the most common Sindarin interpretation, the name consists of the elements hall- "exalted, high" and brand "noble, admirable, fine." HOWEVER, hall- can also mean "veiled, hidden, or shadowed." Already, just at first pass, it's a great name for a Sauron in disguise, because it captures a duality and ambiguity that keeps you guessing, just like the character himself. It's also a callback to Sauron's first name, Mairon, which means "admirable."
Tolkien often took name roots with Germanic origins for his human characters, particularly the Middle Men. In Old English, hal can mean "a secret place" or "whole, undivided" and brand can mean either "torch" or "sword"--a good combination of meanings, given that the entire Southlands arc revolves around a "lost king" uniting his country, only for it to be consumed in fire by a sword being put in a secret lock. Plus, there's the combination of "torch" and "sword" in brand that evokes smithing, especially with the more Modern English use of a "brand" being a mark that is made with heated metal.
In Old Norse, the name element hall comes from hallr "stone, slab," and much like in Old English brandr means "sword, torch." Again, "stone sword" is a very apt name given that putting the hilt in stone is the way to open the floodgates. AND, I don't think it's any coincidence that there's another famous lost king who pulls a sword from a stone... yeah, they snuck a King Arthur reference in there!
Some linguistics nerd on the team really went, "I am going to give this dude the NAMIEST NAME THAT HAS EVER NAMED. It is going to be multilayered and work in several languages and remain just ambiguous enough that even if people [read: me] are crazy enough to look up its meanings they won't get a definitive answer." And that was so sexy of them, my hat is off to them for doing a fantastic job.
Update: I'm doing more name analyses! You can find them here: Arondir | Bronwyn | Theo