Marathon Man is a Halo 3 achievement, which is awarded for accessing all the Terminals in campaign mode. The achievement is worth 40 Gamerpoints and can be completed on any difficulty, or combination thereof. It is represented by a person with a Marathon symbol for a head, surrounded by a yellow circle and with seven yellow stars (representing the seven Terminals) above him. It is a reference to Bungie's earlier Marathon games, in which terminals were an integral part of the campaign levels: they functioned both for providing storyline, guiding the player, and transporting the player to the next level.
After accessing terminal, the player must wait for the screen to go red then wait until the screen shows another text message and finally press A to scroll down to the very last message (a fragment from a Forerunner message) to show up for the terminal to count as unlocked and contribute to the achievement's progress.
- A player must access seven terminals, another seven reference. An additional eighth terminal can be found on Cortana, however it is not required for the achievement.
- The name of the achievement may be a reference to the 1976 film of the same name, or the 1974 novel it was adapted from.
- Some players reportedly experienced glitches upon unlocking this achievement, which prematurely unlocked the SECURITY-class Mjolnir shoulders.