Kaidan Alenko is a human Sentinel and a Systems Alliance Marine. While serving aboard the SSV Normandy, he was a Staff Lieutenant and head of the ship's Marine detail. He also was an initial member of Commander Shepard's squad. Kaidan is a biotic wired with the controversial L2 implants, which are known to cause severe neurological damage to the user. However, he is fortunate enough to only suffer from occasional severe migraines.