There are many great characters in the anime/manga series GANTZ (though Samurai only appears in the manga, as far as I know). It is a dark, bloody, violent story, but it is full of very human characters who react in hauntingly realistic ways to the horrors they are thrown into. In general, the human characters of GANTZ are forced to fight aliens, but around half-way through the story, a new enemy emerges. The Vampires show up very suddenly in the manga, killing off several weaker "Gantzers" and proving themselves to be both powerful and positively ruthless. Why they want to kill the Gantzers is still unknown, but they are relentless and even sometimes ally themselves with the aliens.
The one Vampire who sticks out the most is Host Samurai. He's never seen without a cigarette in his mouth, and very rarely seen without his sword in his hand. From what we are shown, it's easy to assume he is the leader (or at the very least, high up in the chain of command). Several other Vampires who seemed like prominent members were killed off, leaving only Samurai as a recognizable character among them. Also, he is seen at different points giving commands or orders to the other Vampires.
Samurai's history, age, and motives are unknown. We do not know the circumstances of him becoming a Vampire, or why he is so intent on killing off the Gantzers. What we do know is that he is a force to be reckoned with, successfully killing off what many consider to be the two most powerful Gantzers to appear in the series (I won't name them for the sake of avoiding major spoilers). Not only is he highly skilled with the samurai sword, but he is also a powerful unarmed fighter (as demonstrated by how easily he defeated Akira in their little "match", after Akira had similarly defeated other tough Vampires). He's been seen using guns as well as other devices such as sunglasses that allow him to see the Gantzers even when they are using the invisibility function on their suits.
His personality is unclear, but so far he seems to be very calm, calculating, and thorough. I wouldn't call him uptight, however, as he actually seems relaxed and even a bit "laidback" most of the time.
Something I find interesting is that at times he appears to be very cruel and sadistic (he seemed very amused when telling Kurono and the others that the Oni alien would kill them all, and was present and enjoying the show when the other Vampires were beheading all those schoolgirls and draining their blood into tubs; and since he is apparently high up in the Vampire organization, it can be assumed that he orchestrates such activities or at the very least, could stop them if he wanted). But at other times, it appears that he is not so cruel as he is direct and to-the-point. For instance, he normally kills people (Gantzers or otherwise) in very quick ways, never trying to draw it out to torment the victim. He never seems to gloat or taunt those he has defeated (after killing Izumi, he simply walked away wordlessly). And most interesting of all is that he didn't kill Ryouko, Izumi's girlfriend despite the fact that she was right there in front of him. Shouldn't he be a big concerned that she would tell people about what she saw? Izumi also makes a comment about Samurai not finishing him off, despite the fact that Izumi was clearly dying. This may be a long shot, but perhaps he decided to give Izumi a chance to leave Ryouko with some parting words?
Another aspect of his personality that is easy to overlook is the fact that he might have a competitive, even jealous nature. When Akira tried to get the schoolgirl with the dark hair out of the "club" and to safety, Samurai stopped him. He referred to her as a "prize" and said that Akira could have her if he could defeat him. Of course, Samurai easily defeated Akira and dragged the girl off. Most assumed that she would simply be killed like the others, but later in the manga she appears by Samurai's side, a Vampire herself. Why didn't he kill her? What made her special? In my opinion, he only wanted her because Akira wanted her. By turning her into a Vampire and keeping her by his side, it was his way of throwing it in Akira's face. It was like saying "I got the one you wanted!" Because of this, I think Samurai is competitive, specifically with Akira. Being as strong as he is, Akira is probably one of the very few Vampires who can even compare in strength to Samurai (maybe he thinks that, in time, Akira could surpass him?).
Speaking of Akira, I don't think he's actually dead. As many others have said, it's highly possible that Samurai used some sort of device or trick to create a replica of Akira's head, to enrage Kurono. I believe that Akira may have tried to stop the Vampires from going after Kurono, thus revealing that he is indeed Kurono's brother (not hard to figure out, by the way; they have the same last name and look very similar XD). Samurai has attacked him, leaving him beaten on the floor and perhaps thrown in a taunt about how he intends to kill Kurono. Akira has then been locked up somehow to keep him from interfering. Of course, that's just my theory. Akira could be totally dead. I just find it hard to believe that so much time would be spent on his development, and so much hype would be built up around him, only to have him die an off-panel death without anything major happening involving him. I guess we'll just have to see!
END SPOILER WARNING
I decided to name the fanlisting "Recoil & Grace" because I think that phrase really suits Samurai. He is a suave character who moves very gracefully in battle. He seems very classy to me. And yet, he is a Vampire who has killed countless people with no signs of remorse, which is something people would generally recoil from. The phrase "Recoil and grace" comes from a song I have over-quoted to the max lately, "The Beginning is the End is the Beginning" by the Smashing Pumpkins. Go listen. It's that awesome.