Aldarion
Archmage
Personally, I find secondary/supporting characters oftentimes far more interesting than main characters (although in some cases they could even be counted as main characters, just not main main):
- Denethor in Lord of the Rings
- Saruman in Lord of the Rings
- Aberforth Dumbledore in Harry Potter
- Aegon / Young Griff in A Song of Ice and Fire
- Davos Seaworth, though his status as "secondary" character is questionable; that being said, while he is a POV character, he does not drive the narrative the way Stannis does
- Lady Stoneheart in A Song of Ice and Fire
- Sandor Clegane in A Song of Ice and Fire
- Razor in Infinite Sea
- just about every Canim in Conex Alera; will likely develop a more comprehensive list once I actually start reading the series instead of skimming through