The Unstoppable medal (Immovable Object medal in Halo: Reach) is awarded and achieved when any player gets 10 kills in a row as the Juggernaut without dying when playing a Juggernaut game variant. It is represented by a silver star shaped medal with a purple Spartan helmet in the center.
When someone gets this medal the announcer will say, "Unstoppable!" (or, "Immovable Object!" in Halo: Reach) to the player that received this medal. This medal is very hard to achieve in Halo 3's Matchmaking because Juggernaut matches only go up to 10 kills. Killing the Juggernaut to become one will add a point to a player's score, but since he/she was not the Juggernaut at the beginning of the game, it will not count as one of the 10 kills needed for the medal, Unless you do it on a Custom Game.
- The easiest way this medal can be earned is by camping with a strong weapon and take out the enemies if they come at you.