I was wondering this because I noticed that when going through the server node, he seems to hint at the possibility that he was the first geth to arm himself. Does anyone have a solid answer to this?
According to the Mass Effect wiki:
[Legion] was created and dispatched following Commander Shepard's destruction of the Old Machine "Nazara", known to the rest of the galaxy as the Reaper Sovereign[...]
Since Shepard already fought armed Geth (the Heretics) before his encounter with Sovereign, it is impossible for Legion to be the first armed Geth.
You're referring to the Geth that picks up a Black Widow-style sniper rifle, and the implication that Legion was that Geth.
I don't think it's really a sensible notion because, as Legion says many times, there is no real sense of individuality within them. It's possible that some of the same processes that are now within Legion were in that mobile platform that picked up the rifle, but to say it was Legion him/itself doesn't really make sense.
It is in fact Legion. If you look at the other geth throughout the series you can distinguish the foot soldiers, pyros, rocketeers, and primes by their build. Soldiers are the smallest where primes are the largest, as well by the look of the platform. Soldiers are base line no real features that stand out (for geth), Rocketeers have what looks like a light beam on the side of their head, Pyros look like they wear a welding mask, primes have what looks like two wings/pylons one on each shoulder. Now compare them to Legion. It has the single pylon at the shouler, and the larder paulderens on the shoulders (the same as the geth shown in the memory to be arming itself) It uses the same widow class sniper rifle (again the one tha armed itself), and we know from picking up on Rannoch during the Jamming tower mission that the Geth had moved to the Javelin sniper rifle.
Legion doesn't come out and say "Why yes you astute meatbag (giving some love to HK-47) that is me" but does hint at it in the way he talks about the sniper rifle in response to Shepard. Now I know it's feasable that it's not legion but BioWare is known for their easter eggs inside easter eggs methods, so it is very safe to assume this is in fact legion. Remember he did take Damage on eden prime so he may of lost memory or it may of corrupted. The face he still uses the same rifle is indicative of his setimental attatchment to it. Remember Geth are AI fully self aware, and growing, evolving. Like EDI it's easy to see where they would form bonds, or atatchments. While there may be no sense of individuality within the Geth Legion is very indiviualistic. From the "does this unit have a soul, to his use of the personal pronoun "I". While legion is many process in one I believe that the core process the one that speaks for all in that platform, the one that has evolved into the Alpha or individualistic process is in fact the one in the memory.