I just finished reading the chapter of The Silmarillion devoted to Beren and Lúthien, which contains the greatest character in all of Tolkien's work, in my opinion: Huan, the Wolfhound of the Valar. He catches arrows midflight; kills countless werewolves; beats the living snot out of Sauron; scares Morgoth silly; turns on his former master when said master attempts to do evil; lets Lúthien ride him like a horse; dresses himself in a werewolf's hide to travel incognito; talks, but not so often that it gets annoying; never sleeps; and so on.
Huan and Sauron
Sadly, he sacrifices himself to save the people he loves, and as a misanthrope who adores dogs more than anything else in the world, I need to know what happened to him afterwards.
Did Huan go to the Undying Lands, or even get reincarnated on Arda to hang out with Beren and Lúthien some more?
Beren, Lúthien, and Huan (source)