Just 1 character? It's hard enough limiting it to 25, but I think in the end I have to say Steerpike, from Mervyn Peake's Gormenghast.
Of course huge numbers of others deserve mentions (I'll try not to do more than one from each series - Captain Quire (Gloriana), Anasurimbor Kellhus (Prince of Nothing), Elric, Raven (Black Company), Thomas Covenant, Fitz (Farseer), Paul Atreides (Dune), Raif Severance (Sword of Shadows), Joseph K (the Trial), Gray Mouser (Lankhmar), Tyrion Lannister (ASOIAF), Uther Doul (the Scar), Jant Shira (The Year of Our War), Severian (Book of the New Sun), Ganelon (Amber)).