According to itself, Skynet, a self-aware 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 origin.
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 character can complete a small quest to acquire a body for Skynet to download itself into, it will join the Chosen One as a companion.
Skynet 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.
When installed with the cybernetic brain, Skynet is proficient with large pistols (14mm & .223 pistols), SMGs, rifles and shotguns. It also attacks in melee combat with its arms. It compensates its inability to wear armor with a steel structure giving 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 cannot be healed with First Aid or Doctor skills. It is possible, however, to heal Skynet through Repair (works like First Aid). Skynet can also be given any combat commands and actions desired, although as previously stated it cannot heal itself in combat in any way.
Skynet can also 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 exploring every floor anyway.
Skynet does not have total control over the base's security systems and can only reset rather than fully deactivate them. As a result, the Chosen One can still turn robots in the base hostile even after joining forces with Skynet. The dialogue about "there are two Skynets" as well as the base evacuation notes imply that this is due to the rushed manor in which pre existing security systems were placed under Skynet's direct control when the facility was abandoned.
It can be difficult to speak to some non-player characters with Skynet in company. Because Skynet's arms count as weapons, non-player characters who do not speech with armed people will notice Skynet and refuse talk. Thus, for some non-player characters the only way to speak to them properly is without Skynet in company.
If angered (by lying about being Dixon or sarcastic when using computers) and then acquired as an non-player character, right after leaving the base Skynet will kill one companion and then turn hostile.
The organ extraction room in the bottom level can be used to obtain a brain. Regardless of which species is chosen to extract from (even the scratched in deathclaw option), the result will be a human brain.