I have a recollection of a relatively short (20 pages?) comic I read somewhere in the mid-2000s, 2005 to 2008 most likely. It was in a magazine, in color, probably mainly aimed at children/teenage boys. The magazine was published in France, but given the plot and general feeling, it's possible that it was originally published in the United States (which might then have been released a bit earlier than the 2000s).
The first page had the main character, a typical Action Man/G.I. Joe-looking figure, riding a bike or a sports car with a sunset in the background. The narration insert stated that the action was taking place in the Cayman Islands, the Bahamas, Panama, or somewhere which I later would know as a tax heaven. I seem to recall it being an island, not a mainland.
The main character was an action figure with a mission of sorts. I remember feeling this was probably not the first issue, as he was not (or briefly) introduced; but maybe it was just a one-off story not bothering too much.
The most identifying detail I remember is the hero entering a warehouse/mountain/cave and facing the villain, who turns out to be two villains in one: the main villain has an additional face on the back of his head, much like Voldemort in the first Harry Potter book and movie:
I remembered it as being an Action Man comic, and the Dr X/Island X arc sound similar but I can't find much info on it, and certainly no double-faced villain (it's not DC's Two-Face, either). On the other hand, I'm relatively sure the magazine had Action Man on the cover, so if it's not Action Man it might have been something also published by Panini.
I browsed a couple comics available on this page, but the drawing style does not ring a bell. Of course, I might just have skipped the one where the artist changed and drew this unknown two-faced villain.