Echo Three was a codename for an ODST stationed in Seongnam, Korea, to help test the MJOLNIR Mark VI armor.
Spartan-062, the first Spartan to test the MJOLNIR Mk VI armor, was sent in training with several ODSTs. During the armor testing, Spartan-062 hurled a paintball grenade onto the middle of the unsuspecting ODSTs, neutralizing Echo 1 through 5. The sole survivor of the blast, Echo 6, made a run for it and was quickly gunned down by 062, but not before initiating the "Bulgoki Gambit". After Spartan-062 was subdued, she was brought back to the Special Ops Center, accompanied by Echo Three and his ODST companions (whom all had paintball marks on them).