Since its founding in 1831, the Legion has become the one place of escape for those with haunted pasts. Men with criminal records, shady business dealings, or deserters from their home country’s armies were accepted into the ranks, with no questions asked. Stripped of their old identity and given a new one, the new legionnaires are able to begin their new life with the slate wiped clean.
The French Foreign Legion is willing to let you join up under an assumed name. However, first you’ll have to tell them who you really are, and French police/intelligence services will do a check. If you’re wanted for something relatively minor, or let’s say running away from debts, they may overlook that and let you start a brand new life, with the possibility of acquiring French citizenship at the end of your service. But if they find that you’re wanted for murder, you can expect to be arrested and extradited.
The new name is just for administrative purposes and to give the legion plausible deniability if anyone comes asking about you.
Even if you take a new name (and the policy on requiring or not requiring a new name changes every couple years), you must be rectified so that you take back your real name (with a certified birth certificate from your home country with your real name) so that you can get credit for your courses and deployments and so on.
I have heard that you can’t deploy until you get rectified, OR that you won’t get credit for retirement for any deployments until you are rectified (someone serving can clear that one up). So, if you stay for a career it is essential to go back to your old identity. Some guys stay under an assumed name for years due to hiding from the law but those are rare cases and eventually, you need to go back to your old name if you want to go on deployments or stay until retirement.
The French Foreign Legion will still accept deserters and other minor miscreants, but it’s not as easy as it once was. New recruits are given a battery of physical, intellectual, and psychological tests before they even get any kind of training. Later on in the process, recruits are screened for “motivation” in order to weed out those who don’t have the drive to make it in the ranks.