According to himself, Skynet, a new thinking computer, was conceived and developed in the year 2050 through the use of alien technology. In the year 2081, 4 years after the Great War, Skynet became self-aware. In 2120 Skynet was given a new set of instructions and then abandoned by its makers.
Skynet's records are most likely partially or entirely incorrect. According to other sources, Skynet became self-aware in 2075. It also was not created as early as 2050, since the first artificial intelligence was made in 2059. However since it was created using alien technology, it's quite likely to have been a military research project and any records of it were classified and then changed to prevent anyone from learning its origins.
Skynet is bored with administering the depot by 2241, it having been 164 years since there was any real activity on base. It seeks to travel and learn about the world. Assuming the player can complete a small quest to acquire a body for Skynet to download itself into, it joins the Chosen One as an non-player character.
He left the Chosen One and began to travel west into the wasteland, looking for terminals and data to acquire more knowledge, collect more data, and perhaps "settle down" in a mainframe. The frame he was in, and the brain he had could only store so much information, and AIs need more data storage space to grow in order to evolve. It is possible he made his way to the Glow.
Acquiring Skynet requires several items on the player's part to activate what will become Skynet's body (see main article).
Skynet will join the player as an non-player character, assuming they have room.
When installed with the cybernetic brain, Skynet is proficient with large pistols (like 14mm pistol and .223 pistol), SMGs, rifles and shotguns. It is interesting to note that even though skilled in using large pistols, Skynet refuses to equip the .223 pistol. It can also attack in melee combat with its arms. It cannot wear armor, but its steel structure gives it protection equivalent to Metal armor Mk II. Skynet can also instantly repair all damage to itself outside of combat (via a dialogue option, like other NPCs). As a robot, stimpaks naturally have no effect on it and you cannot heal it with First Aid and Doctor skills. It is possible, however, to heal Skynet by using Repair skill (works like First aid). Skynet can also be given any combat commands and actions the player wishes, although as previously stated it cannot heal itself in combat in any way.
Skynet is also able to carry 225 pounds of equipment.
As well, when exploring the Sierra Army Depot, Skynet will automatically deactivate security systems on each floor upon entering them, a rather moot point, since acquiring it as an non-player character forces the player to explore every floor anyway.
Skynet doesn't entirely control the security systems directly.
It can be difficult to speak to some non-player characters with Skynet in the party. Because Skynet's arms count as melee weapons, speaking to non-player characters who will not speak to you when you have a weapon out, they will see Skynet and not talk. Thus, for some non-player characters the only way to speak to them properly is without Skynet accompanying you.
If you anger Skynet and then acquire it as an non-player character right after leaving the base, it will kill one of your party-members and then turn hostile.
You can also use the organ extraction room in the bottom level to obtain a brain. Regardless of which species you choose to extract from (even the scratched in deathclaw option), the result will be a human brain.