Hellsing Ultimate is a show driven by killing. The good guys kill the bad guys because the bad guys were killed by even badder guys who kill because they themselves are dead and that's just what dead people do.
So it makes sense that at the top of this kill-stravaganza is the one man who cannot be killed, in this case a vampire named Alucard.
Alucard is the prime field agent for the Hellsing organization, a secret organization devoted to protecting England from the forces of the undead because apparently the rest of the world can just go die in a hole somewhere. During a routine mission, Alucard deems it necessary to blast a hole through a police woman in order to hit the vampire behind her. As this was totally unnecessary and completely dickish, Alucard offers to make her a vampire and she accepts. He then travels the countryside accompanied by his plucky sidekick Seras Victoria, defeating hordes of undead abominations while looking as badass as possible.
Make no mistake, Alucard is the star of the show here. There are plenty of other characters in this show that challenge the badass status quo, but none of them can come close to Alucard's blatant disregard for the laws of mortality. His response to being shot about 40,000 times is to brush himself off and proceed to tell you how useless and pathetic your efforts are. His thoughts on decapitation and dismemberment are basically 'hahahahahahaha, nice try'. One would assume that upon being ripped apart at molecular level, he would simply reconstitute himself into the shape of a middle finger and proceed to rip your skull out of your ass.
At this point you may be asking yourself, 'why should I care about someone who fits the description of Jason Vorhees?' Because the show demonstrates his immortality very tastefully. His numerous reconstitutions are never met with annoyance, but rather excitement. And as he takes injury after injury, blow after blow, shot after shot, you start to get the impression that he wants to die. That he has grown bored with his everlasting permanence and wishes to end his immortal life. That all he desires in the world is the person who is strong enough to kill him and allow him the peace of eternal sleep. And you begin to wonder, when he finds this opponent, the one person in all of the world who can grant his deepest desire, will he surrender to the lure of the afterlife, or will he fight to protect our world?
And then he blows the guys head off and you quickly forget about that. Hellsing is fond of Devil May Cry school of awesomeness in that being really hard to kill doesn't mean you don't have to dodge and that normal people can dodge bullets if they are awesome enough. The story moves quickly and is never boring, and it is interesting to see Seras come to terms with her new status as one of the undead.
So if Hellsing Ultimate sounds right for you, consult your local anime provider.
