Existing Characters

How important are characters/performers in music videos/short films?

I think that characters are the second most important aspect of a film, following on from narrative. Characters can help the audience to better understand a narrative through the use of body language and emotion. If the character is looking sad then we know that the narrative is unlikely to be comically based and that it probably has a more serious meaning behind it.

Existing character profiles -
The Joker is an American villain in the Batman films and in this series he is played by Heath Ledger. He is a violent psychopath that chooses to kill innocent people for his own entertainment. He could be considered to be quite a lonely character as the audience is never told about his family or past and we always see him by himself in the films. It could be said that Batman is Joker's only 'friend' in the sense that the Joker needs Batman to keep him mischievous and depriving Gotham City from its joy and happiness. So, without Batman keeping things in Gotham in order, I don't think the Joker would be around to mess things up with his elaborate plans.
Overall I think that the Joker is a great asset to the Batman films and Heath Ledger's portrayal of him makes the character even more amazing and enjoyable to watch.

The Joker is one of the main characters of the series and so the audience will pay a lot of attention to him. In some cases the audience may feel like they are involved in the scenario and so feel frustration or anger at certain things that the character does. He is an iconic character as he is portrayed by a very talented actor, Heath Ledger, some saying that he did the best portrayal of the twisted character.
With this character Ledger was also able to mimic any personality or behaviour perfectly. For instance, in a scene in The Dark Knight we see the Joker dressed up in a nurses attire whilst he talks to Harvey Dent (the video below).

Eddie the Head is the mascot of the British heavy metal band, Iron Maiden. Eddie is an iconic character that features in some of the band's music videos. This is a memorable music video character because it is unique and not many other bands have a character that frequently features in their music videos.

The video above is of Iron Maiden's song 'Speed of Light', in which we see the character of Eddie travelling through different iconic games.

Leonard Shelby (Guy Pearce), from Memento, is an ex-insurance investigator, who left his job after suffering an attack from the rapists and murderers of his wife, which left him with brain damage and the incapability of creating new memories, with the last thing he remembers is the death of his wife. The film situates him on the hunt for the killer of his wife, but his amnesia is a massive obstacle that he struggles to get over throughout the film. 
Leonard is a very smart character, and figured out a system that allows him to send messages to his future self, who will soon forget that moment had ever happened. He does this by taking polaroid photos of people and places of interest for his investigation, and as for clues to his wife's killer, he tattoos himself in order to have permanent notes that he can't lose. These acts show his intelligence, and we can see that his has gotten use to losing his memory every few minutes or so, and that this system is a clever way of keeping up with his own journey.