Jan had dark skin, amber eyes, and dark hair. He wore a dark blue high-collared jacket and dark blue pants, both of which had white trim. He also wore white gloves and a dark blue cap with a white-and-gold eye design on the front.
Jan is notable for having multiple gold piercings: some in each ear, his nose, his eyebrow, his cheek and two on his lower lip. Later, one of the piercings on his lip is ripped out by Walter's microfiliament wires in their battle at the Hellsing mansion.
The description of Jan in the author's notes at the end of manga Volume 2 jokingly imply that he has a number of hidden piercings.
Jan is shown to be vulgar, rude and one of the most foul-mouthed characters in the show, constantly spewing profanity at others and making volatile comments about them. He is also perhaps the most obnoxious, given the fact that he's often loud when he speaks and laughs quite often, even in the face of defeat or death. Unlike his brother, who is usually composed and focused on maintaining their family's business, Jan appears to not truly be pleased unless he is enjoying himself by causing chaos and destruction. This and his appearance make him the complete opposite of his brother. It is implied that he and his family come from an extremely poor background, as Jan said "he knows how to rise from the bottom".
Jan Valentine leads a force of ghouls into the Hellsing Headquarters when the Knights of the Round Table held a meeting at the Hellsing complex concerning a course of action on the new vampire "freaks". The purpose of Jan's attack is to assassinate Integra Hellsing and the Knights of the Round, but mainly to create chaos and disorder within Hellsing.
He appeared to have succeeded in this latter mission, as during this battle, over three-quarters of the organization's army was killed or turned into ghouls themselves. Jan was the only member of the attacking army to ever reach the high-security meeting, as the rest of the ghouls were destroyed by Walter and Seras. There, Sir Integra and the Convention of 12 congratulated him, before opening fire and riddling him with bullets
He is later seen being beat up by Walter. When questioned by Integra about his origins, he reminded her that the chips in his body were still transmitting information to his commanders, including everything that was being said. He then asked her if she thought that considering he and his brother didn't succeed in destroying Hellsing, and that his superiors knew that he was about to tell them everything he knew, they would let him live. Immediately after that, he bursts in flames. As a final, mixed act of disrespect and help, he gave integra the finger and uttered the word "Millenium" before disintegrating.
In the Hellsing anime, Jan was sent by Incognito to incapacitate Hellsing so that he could release Sett on London, England. In the Hellsing: Ultimate OVA, he was sent by Millennium to destroy Hellsing. In the last volume of Hellsing we see his hat representing his shrine (with his brother's knife too) along with the items of the other people who died.
The Valentine Brothers were made specifically to eliminate Hellsing, with Jan being created with the purpose of wiping out the entirety of the Hellsing forces other than Alucard. Due to this he was designed to lead ghouls into combat and did this to great effect - wiping out the primary infantry of Hellsing easily, however the presence of fledgling vampire Seras Victoria eventually caused his downfall and death. As seen among the most powerful monsters of the Millennium Organization he also had a self-destruct ability, which was used by Millennium to disintegrate his body before he could reveal any information on its whereabouts.
He wields dual custom P90s as his primary weapons of choice.
- "Heheheheheh! So this dude's friend, I mean he's like a real doctor but like does the cosmetic shit on the side, right? So then that same crazy fuck with the horn comes back but now he wants a plexiglass plate for his skull! And the doctor fuckin' does it! He makes a window! You can see the fucker's brain and shit! The guy's got a big monster horn and his head meat on display! The guy's a freak, I mean what the fuck!? Hahahahaha...Yeah, get it?"
- "Up up! Down down! Left right left right! Bringin' the motherfuckin' death by Konami. Oh I'm so fucking hard right now."
- "Er...hello? Is this thing on? Cool. This message is going out to the Round Table Conference, and a very personal and heart-felt shout-out to the queen bitch herself, Miss Hellsing! Alright! Your ass is currently being kicked by the Valentine Brothers! My name is Jan Valentine, and I can't wait to meet each and every one of you. We'll be getting intimate as soon as me and the boys finish lunch, so let me be the first to thank you for providing us with these tasty snacks! By tomorrow, Hellsing will be nothing more than a pile of shit. (...) We highly recommend pissing yourselves, followed by a course of praying to your impotent god. But hey you can be a man and kill yourself. Thank you, London, we love you! Good night!"
- "Lil' Hellsing chicky, we're comin' to find you. Come on out, and play "Lil' Hellsing. I promise it's gonna be a lot of fun. We just wanna torture, kill you, maybe skullfuck your corpse a couple of times. Burn the house to the ground, go home and masturbate, okay?"
- "FUCK, these are some fine cigars! Like all bourgeois and shit. I mean c'mon! That's just fucked up! People are starving in the world and she's wasting money on this? A slow and agonizing death is too good for that stick-up-her-ass bitch. I think it's time someone gave her an ol' fashioned workin' class ass kicking!"
- "Damn, that is some fucked-up shit! A country with this much poverty and what does Miss Bitch spend her money on? These fucking overpriced cigars! Don't you boys think that's pretty fucked up? 'Course you think it's fucked up! Death's too good for her. I'm gonna fuck that bitch, shoot her in the head, and fuck her there!"
- "What up, bitch!"
- "See, I so fucking told you! Ha ha ha! Well, since I'm fucked, how about I piss a little wisdom on you dipshits? You can take this clue and shove it up your ass, bitch! Beware...the Millennium!"
- Both the Gonzo anime and the OVA has Jan reciting the infamous Konami Code during their assault on the Hellsing mansion, finishing it by saying "Bringing the motherfucking death by Konami!". The manga version simply has Jan saying "We have a God Mode cheat and you don't!!"
- Jan and his older brother Luke appear in omakes at the end of almost every Volume in the Hellsing manga. These comics take a humorous note and Jan and Luke make completely random comments, talking about the progress of the series' plot and popular video games. The characters in the omake are intentionally poorly drawn and have little detail.
- Unlike his older brother when backed into a corner he continued to fight rather than run away.
- It is interesting to note that the nationalities of the brothers is never made clear, although it seems that they are from the United States, judging by their dialogue in the manga, which is devoid of British phrases such as "wanker" (which at least Jan would've used at some point), or German pronunciations (like "ve" instead of "we"), or, if they were thought to be British, the fact that they don't seem to mind that one of Millennium's plans is to wipe out London.
- Jan's P90s appear to be custom-made. The traditional thumbhole-styled stock present on standard P90s has been largely cut away to make way for a pistol grip as a handle. This is possibly to make dual-wielding them much simpler as thumbhole stocks were originally designed for the shooter to use both hands to handle the weapon, making it hard to effectively use the weapon while one-handed.
- Furthermore, the scope mounts on his P90s are sniper scopes, one of which appears to be based on the Eclan Digital Hunter and the other of an unclear model, although appears to be based on the Leupold Mark 4 and the Zeiss 3-12x56. Quite an odd choice of optics for PDWs.
- Jan's P90s do not show any signs that they are silenced, as noted by the muzzle flashes seen and loud rapport of his gun while firing, despite the large silencers mounted on both his guns. Because of this, they might just be Barrel Extensions, enhancing Jan's accuracy.
- All of these modifications to his P90s, while in fact enhancing their, and thus his, capabilities, would make wielding somewhat difficult for a normal human, and can have one question how he carries one such weapon concealed in the first place, let alone two. Considering his is a Vampire, this point would however be moot.
- His quote "Up up! Down down! Left right left right! Bringin' the motherfuckin' death by Konami. Oh I'm so fucking hard right now." refers to the famous Konami code (Up, Up, Down, Down, Left, Right, Left, Right, B, A, Start). In Contra for the NES, typing this code on the title screen gives you 30 lives.
- Throughout the anime, he is referred to as Yan and in the ending credits of Hellsing: Ultimate X, his name is written as Yan Valentine.