Mjolnir Recon number 54 is the player's designation number. Throughout the Marathon series he is directly referred to as the Security Officer, the Cyborg, or the Marine.
Mjolnir Recon number 54 is a two-meter tall cyborg sporting green vacuum-enabled battle armor. His superhuman prowess originates from his transformation into a MJOLNIR battleroid centuries before, but despite having undergone this process, he is able to blend in with other humans. Aside from the player's unique armor he has no other distinguishing visual features.
He is never directly referred to by his designation: "Mjolnir Recon number 54", but is only referenced indirectly. In Marathon Infinity, the player is also identified as "Conditioned Unit 7" by Tycho.
At the start of Marathon, the player appears to believe that he is merely a human, although clearly a talented, dangerous, and powerful one. However, persistent references to "nine MJOLNIR Mark IV cyborgs" throughout the game has led many fans to believe that the the player is in fact the tenth member of this group. However, the player himself does not come to realize this until Marathon Infinity, when he starts having surreal flashbacks, trips into his own mind, and bizarre dreams as a side-effect of the Jjaro technology employed in his cybernetic enhancements.
The Cyborg's mind and personality are mostly left up to the player to speculate on. Although Durandal describes him as "a magnificent killing machine" and asks him if being allowed to kill more Pfhor will "make you happy," the AI is more likely being malicious than accurate. While the Cyborg does not seem to be a mindless psychopath, he is clearly comfortable enduring and quite capable of carrying out violent acts on a scale unimaginable to any normal person. However, in the third game of the series, he seems to lose any sense of morality he may previously have possessed, working for the indisputably evil Tycho and killing BOBs on Tycho's orders in a desperate attempt to keep the W'rkncacnter trapped in Lh'owon's sun. In Marathon Infinity, we are given greater access to his mind and feelings. He seems to recognize some sort of guilt or weariness for the atrocities he has committed, and appears to believe that he has been forced to do what he has done. Ironically, this seems accurate. All three games consist chiefly of doing what various people tell him to do - only once does he act of his own initiative, and this is in the Marathon manual, which is not an entirely reliable source. The color of the Marine in multiplayer can be changed in settings, but can also be seen by going into third person mode by pressing F6.
It has been speculated that the Cyborg's mind is that of an AI in a human's body, supported by the fact that during one point in Marathon Infinity, the the player appears to upload Durandal's core matrix into his own brain before merging it with Thoth). In Infinity, he seems to be undergoing a sort of rampancy. The three chapters of Infinity are called Despair, Rage, and Envy, which parallel the three documented stages of rampancy -- Melancholy, Anger and Jealousy. Since rampancy is defined as "an artificial intelligence's coming to realize that it is not real," this may show that the player is not, in fact, human. Alternately, it may symbolize the entirely human will wresting control of his own destiny from the AIs that he has been serving for the last three games, and unlocking mastery over the latent powers of the integrated Jjaro cybernetics.
Were you ever curious about the tenth cyborg which was supposed to be on the Marathon? Why could Leela find only nine? Was it ever activated? Was it destroyed during the defense of the colony? You are right to be curious.
- Durandal, Marathon 2: Durandal (Preview), What! About! Bob!, Terminal 1 (2nd message)
Everyone is talking about your exploits on Tau Ceti during the Pfhor invasion seventeen years ago. During those two days I remember hearing the crew talking about a single man, standing alone against the invaders, but I had no idea that it was only through your efforts that the Marathon and perhaps Tau Ceti itself were saved.
-Robert Blake, from Marathon 2, My Own Private Thermopylae, Terminal 1 (2nd message)
- In many ways, the Marine bears resemblances to Master Chief of Bungie's later Halo series.
- Mjolnir Recon number 54 is a MJOLNIR Mark IV cyborg whereas in Halo Master Chief is first seen wearing MJOLNIR Mark V armour (later Mark VI).
- In almost all Terminal artwork depicting him, he always has different armor, sometimes not even resembling his spritesheet.