Spice, if you've never watched Highlander, I'd highly recommend it. It's about immortals.
I know they've done a whole bunch of remakes on the series, though. But the guy in the image is the main character in the one I watched
In it you have to cut off an immortal's head in order for them to die. Then you gain their power, skills, whatever, you're basically a more valuable immortal. The older you are the more "power" you have.