How can Alucard die?

Question

In the Anime "Hellsing", the character Alucard seems to be invincible. Is this just who he is, or does he have a weakness of some sort? And how did the Hellsing Organization catch him in the first place?

Answer 1

In the anime he is basically invincible and he has no known weaknesses but in the manga he eats a character who is "everywhere and nowhere" and this causes him to "disappear" basically as close to death as is possible for him.  How he is caught is suggested that he is Dracula from Bram Stoker's novel but instead of being killed by Van Hellsing ,like the novel, he decides to let him live and become a servant.  

Answer 2

Spoiler Alert! This is from the Manga.

Alucard does die or atleast disappeard. Alucard lives on the souls that are within his body. (Those eyes you see when he transforms are the souls inside him.) Well an enemy implanted a virus inside Alucard when Alucard absorbed a body that contained the virus. Well, in effect that virus somehow made alucards souls disappear making him disappear as well. As of now he is totally gone.

Also his weak ness is sunlight and that he can't swim in water.