While shows normally centre around heroes, individuals who go out there and do what must be done, it's often the villains who propel the story and provide the most memorable moments. Who can forget Alan Rickman's amazing performance in Die Hard (or Robin Hood: Prince of Thieves), Gary Oldman in Leon, Kevin Spacey in the Usual Suspects, Darth Vader and so on. Villains are just as important (if not more so) as the heroes in stories. Without someone to stand up against and constrast with our favourite heroes would be a shadow of their former self.

Lets face it, everyone loves a good bad guy, it gives you someone to either root for or rail against, and television is no exception to this. There have been some exceptional villains on screen over the years and here is a selection of my favourites.

Number One/John Cavil
From Battlestar Galactica. Portrayed by Dean Stockwell.

More than any other cylon in the show it's Cavil who stands out as the primary antagonist and most dangerous threat to humanity. A Machiavellian individual who not only threatens the humans, but also stands opposed to any cylons who attempted to get in his way. Lacking any kind of mercy he was responsible for the fates of the final five cylons, tormented Ellen Tigh terribly on New Caprica and constantly called for the culling of humans wherever possible.

He provided a face, voice and name for the threat the Cylons posed, while also turning out to be mostly responsible for the conflict between humanity and the Cylons as well.

Lieutenant Jon Kavanaugh
From The Shield. Portrayed by Forest Whitaker.

Strictly speaking Kavanaugh is not a villain as such, but because of the unusual perspective of The Shield he is cast as one. Sent to investigate allegations of corruption amongst Farmington's Strike Team he is diametrically opposed to the series' anti-hero/protagonist Vic Mackey and his team. Kavanaugh is powerfully portrayed by Forest and charts a fall from grace as he becomes increasingly more and more desperate to find evidence that Vic Mackey is corrupt. His tactics become more agressive and gradually he is drawn into breaking the law in order to try and do what he feels is right.

It's this 'the ends justify the means' attitude combined with the powerful and intense performance from Forest which makes Kavanaugh a gripping villain and a worthy foil for Vic Mackey.

Maurice Levy
From The Wire. Portrayed by Michael Kostroff

Maurice Levy originally surfaces in The Wire as the lawyer responsible for D'Angelo Barksdale's case, it's his defense (combined with intimidation from the Barksdale organisation) which results in D'Angelo being released. But this rather innocuous initial appearance conceals someone who is far deeper into the world of crime than anyone would or even could suspect. As time passes it becomes clear that he's a major source of advice to the criminal world, assisting Avon Barksdale, Stringer Bell and even Marlo Stanfeld as time passes.

It's this corrupt and unscrupulous attitude combined with his 'light touch' which makes Maurice such an interesting villain, he's like the proverbial slippery eel. It's clear he's involved in crime, but because he has such a complete grasp of the law he's very difficult to pin down. He's dirty and almost untouchable...

Avatar
From Millennium ("The Mikado"). Portrayed by unknown.

Avatar is unusual when compared to the vast majority of villains in this list as he only made a single appearance in the second season of Millennium. Modelled around the Zodiac Killer, Avatar also communicated with the police using cryptic messages and was a dormant serial killer who had just resurfaced with a new modus operandi - killing his victims according to the number of hits his webcam site received. People who were visiting the site to see what was happening were quite literally facilitating the death of the victim on camera. Eventually the series of clues Avatar left for Frank lead into two traps, one of which took the life of a police officer and the other which nearly resulted in Frank shooting an innocent woman.

Little more is known about Avatar as he was not caught by Frank and the police force (like the Zodiac Killer) and as the show never revisited him he remains at large. Which is a big part of what makes him so interesting, he's still out there, on the loose, waiting to strike again.

The Greek & Spiros "Vondas" Vondopoulos
From The Wire. Portrayed by Bill Raymond and Paul Ben-Victor

The second villain(s) from The Wire on this list, The Greek and Vondas first make their appearance in The Wire's second season as the men behind the smuggling which Frank Sobotka was facilitating through his docks. Vondas is initially revealed as the head of the organisation through meetings which occur in a small diner. But a little while later on it becomes clear that the innocuous old man who is seen dining there all the time is in the true head of the organisation - The Greek.

The pair are the personification of prudent and cautious criminals, for them it's about "Business, always business." They are willing to deal with whomever has the cash to purchase the product and they are efficient in their role as drug wholesalers, human traffickers and large scale thieves. In fact there are few pies they don't have their hands in.

Of the two it's Vondas who is the softer, he forms quite an attachment with Frank and especially Nicky Sobotka. But if there is any killing to take place it is Vondas who will do the deed. The Greek on the other hand tends to keep his hands away from anything dirty, but is ruthless when it comes to taking care of business. If The Greek feels you've become a threat to himself and his operation then you won't last much longer.

Davros and the Daleks.
From Doctor Who. Portrayed by Various.

Quintessential Doctor Who villains the Daleks and their creator just have to be present on any list mentioning top villains. The murderous salt and pepper pots have menaced the Doctor (and countless children positioned behind the sofa) for longer than any other villain on this list.

There's something just so iconic and incredible about them, considering that they are little more than slow moving condiments with a plunger, a whisk and bunny ear lights on their heads. Their attitude and catchphrase of "Exterminate" moves them away from the comical and into the frightening. Daleks represent the purest form of racism, so far gone that they seek to destroy everything which is different to themselves. They are the equivalent of a man sized virus or plague; so virulent that not even the Doctor's repeated attempts to stop them has ever had any long term effect. They keep coming back and they will continue to do so as long as the series runs.

Nina Meyers
From 24. Portrayed by Sarah Clarke

You can draw a direct link between the quality of 24 and the presence of Nina Meyers. The first season was just fantastic and the gradual realisation that Nina was a double agent is a huge part of that, her shooting of Jack's wife is amongst the best ends to a season ever. But then in season three Jack encounters her again and shoots her dead - while it's an understandable action it also signals the start of the reduction in quality the show has. I didn't even manage to watch all of the rest of season three and every attempt I made to watch each season following resulted in failure.

The lack of Nina probably isn't responsible for the downward plummet 24 has taken, but the show would have been a lot more interesting if she was still around in some fashion. It feels like the pay off of Jack killing Nina would have made for an excellent show finale. But it was not to be like that, which in some ways is realistic, but in others clearly bad for the show's performance.

Old Yellow Eyes/The Yellow Eyed Demon
From Supernatural. Portrayed by Fredric Lehne

As the primary antagonist for the first two seasons of Supernatural the Yellow Eyed Demon (Azazeal) was responsible for the vast majority of the sorrow and torment the Winchester family suffered over the years. Both the boys mother and Sam's girlfriend were slain by Yellow Eyes. Almost unkillable, vicious, evil and ancient beyond measure he was a terrible opponent for the Winchesters. Even after the Winchesters defeated him his presence and plans continue to make themselves known and felt. While he didn't count on being slain, as demons are supposed to be immortal, dying hasn't stopped the wheels he set in motion.

He also had a dark and amusing sense of humour about everything, often taunting the Winchesters and even willing to banter and converse with them. Fredric Lehne brought a lot of presence and 'cool' to the character and made him much, much more than just "the enemy".

Honorable mentions:
Shane Vandrell (The Shield) who didn't make the cut because a) he's not a villain the entire time he appears in the series and b) I'd already picked one character from The Shield.

Antwon Mitchell was cut from the list for a similar reason.

Ben Linus from Lost also has a similar bent in that he's not strictly speaking a villain, as time passes he becomes more of a protagonist with his own agenda.

The Master from Doctor Who, again excluded because the Daleks had already taken a spot.

Sylar didn't make the top list because it feels like Heroes has done it's uttermost best to reduce the impact of this character by sucking hard. Zachary Quinto's performance as Sylar is one of the two best parts of the show, but he is stuck on a sinking ship now.

Captain Hammer from Doctor Horrible's Sing Along Blog also didn't make the cut. Strictly speaking he's a hero. But he is the villain of the piece, regardless I do hope he makes a return appearance in the next Doctor Horrible.

Spike from Buffy and Angel. Who lost out because he becomes somewhat redeemed and shifts into the position of anti-hero as time passed on. His wiry observations remain amongst some of the most entertaining in the shows.

So that's my list, but I'm sure there are many, many more who could and should have made these lists. Who are your favourite television villains and why?