Taken (film)/WMG

It's all an extreme case of Even Evil Has Loved Ones.
An Alternative Character Interpretation I've thought of...What we're given of Bryan's past, and indeed some of how he acts now that It's Personal, could easily indicate that he is, if not necessarily a Retired Monster, at least someone who could easily have been the villain of another story in his younger years.

Jean-Claude will factor in the sequel
Somewhat implausible, but maybe the guy is forced to work with the albanians or something.

Bryan Mills is secretly Hannibal
Obviously, Taken takes place during a temporary retirement, and after the whole mess with rescuing his daughter, he went back to his old job after realizing that it's what he was meant to do.

Bryan is not finished yet...
We have no clues that Bryan stopped killing human traffickers at the end of the movie. It's perfectly possible that, after he's spent some time with his beloved daughter, he'll just get back to business and kill the rest of the organization. After all, they know to much, and they weren't exactly nice towards his daughter, so he has a good reason to finish them off. And when the streets of Paris are drenched in the blood of the traffickers that were foolish enough to think they cound handle a war against hells most prolific servant, he'll leave the terrified city and declare another war on all the criminals of the United States. And then, he'll meet Frank Castle. It won't take long for them to kill every single criminal in the world, and soon, hell will freeze and the darkness itself will whisper the name of every single grieving mother they have created, and the laughter of the dark gods will be silenced when they gaze into the eyes of Bryan and Castle. The world will never be the same again... and all of this because some asshole thought it would be hilarious to kidnap Bryans daughter! Thank you, fucker!
 * As far as This Troper is concerned, this is Canon. Even Word of God will not be able to contradict the canon status of this.

Liam Neeson's character in Unknown is Bryan
Come on,, only this time with amnesia. His line "I didn't forget everything, I know how to kill you, asshole" is pure Bryan.
 * I agree, maybe it was even a prequel. Even my mom thought it was part of the Taken universe when she watched it.

That guy tied to the chair is not dead...
You remember that guy who was tied to a chair and tortured by Bryan? At the end of the scene, Bryan turns on the switch one last time before leaving the room, letting the poor guy burn. You know what I think? I think he's still sitting on that god damn chair!