"The Last Centurion" isn't a standard Magic keyword or ability—it doesn't exist in the official rules or on any printed card. It sounds like it could be a custom card name, a flavor reference (possibly to DoctorWho's Rory Williams, "the Last Centurion"), or a homebrew/joke card from outside official Magic products.
If you encountered this on a card, check whether it's a custom/proxy card, an Un-set or Secret Lair novelty, or something from another game entirely. Magic cards have their actual rules text printed in the text box, so read that text and resolve it normally—the card's name carries no inherent ability.
For Commander specifically: if it's a custom card, confirm with your playgroup before using it, since unofficial cards aren't legal in sanctioned play and need table agreement in casual games.