Liam Neeson is Bryan Mills, a retired CIA "preventer".    From Wordnik.com.  [Film.com Movie Blog] Reference

Liam Neeson stars as Brian Mills, who was a CIA "preventer," as he calls himself.    From Wordnik.com.  [Crimson White RSS] Reference

We also get a taste of Mills 'skill as a "preventer" when he takes a quick job as a bodyguard for a pop-singer who is in town for a concert.    From Wordnik.com.  [Cinema Blend Feeds] Reference

Mills had only recently given up his government career as what he calls a "preventer" to be near Kim, who lives with Bryan's ex-wife Lenore and her new husband.    From Wordnik.com.  [Starmometer.com] Reference

"preventer" to be near his daughter Kim, who lives with Bryan's ex-wife Lenore and her new husband.    From Wordnik.com. Reference

We fired the preventer, but it didn't work for beans.    From Wordnik.com.  [Week 880: Our most famous neologism contest, and the winning oil spill song parodies] Reference