Just 'tête marteau' (as in 'vis tête marteau' or 'vis à tête marteau) is routinely used when referring to hammer-head screws/bolts, too, BTW.
Could work, too.
stevenc and side.g correctly point out that 'du' implies reference to a specific object rather than a general one.
I kind of obfuscated that point, I admit.
'Marteleur' still gets my vote. Significantly more comprehensible, and rolls out just sounding cooler.
Another thought, adding to the above, while I'm busy overthinking this: 'tête de marteau', while it doesn't carry this possible usage/connotation in French as far as I'm aware, is so close in form to expressions such as 'tête de cochon' (hard-headed or disagreeable, literally 'pig-headed'), that in the context you propose to use it, I might, on first sight, read it as 'hammer-headed' rather than as 'hammer head'. 'Hammer-headed' in English (the insult makes an appearance in Dirty Harry) basically means hard-headed or 'thick', of course.
Hence I tend to think that Citoyen du Monde points in a productive direction...really fits with your description of how 'Hammerhead' came to stick as a nickname back in the day.
EDIT: I see Lewis_Moon hardly needed the further convincing!
Last edited by mikemowbz; 08-27-12 at 01:36 PM.