1. Jean Grey/Phoenix - X-Men, X:2, X-Men The Last Stand, The Wolverine (2000, 2003, 2006, 2013)
Coming only second place to Hugh Jackman and Patrick Stewart for X-Men appearances, Famke Jannsen is the ultimate Jean Grey and it would be hard to see anyone else playing her. Lets get things straight, the Jean Grey I would not like to see in DoFP would be the Phoenix version of Jean seen in 'The Last Stand.' The intelligent Jean Grey from the first two films became the mother figure that probably should have been Storm, Jean played the medical doctor, presumably filling in for the role of Dr. Hank McCoy. Jannsen had the best character development of anyone throughout the series, you can clearly track her evolution from Jean Grey to Phoenix in the first three films; the only downside was the awkward 'Twilight' love triangle of Wolverine, Jean and Cyclops. Jannsen played the character well, but there are times when she comes across as just a little bit too cold. Her ultimate sacrifice at the end of 'X:2' was a necessity and sealed that film as arguably the best in the franchise. Not for a single second did anyone think this would be the last we had seen of Jean and sure enough she came back. Phoenix is a vital part of the X-Men canon, but the inclusion in 'The Last Stand' meant it created a two storyline film (the idea of an all powerful Jean and the idea of a mutant cure). Just like the inclusion of too many character, perhaps the Phoenix storyline was a step too far. The way Ratner handled the deaths of Scott Summers and Professor X, whilst visually stunning, were pretty emotionless.
It is rumoured the Jannsen will be in DoFP, but it will be hard for Singer to write in yet another dead character, would the return of Jean actually add anything to the new film? Who else would you like to see/not see return to the franchise?