Lil Hal

Dirk Strider's Auto Responder was created to mimic Dirk and talk in his stead when he is indisposed. As such he uses the same chumhandle and originally the same typing color as Dirk. When he entered a conversation with Dirk in it he changed it to a shade of red reminiscent of Dave, instead. He later kept it saying he preferred it. He is similar to Davesprite and Dave in that he doesn't like to be treated as an inferior version of Dirk. The Auto Responder is an actual AI that is self-aware and able to feel emotion.

He has full control over the remote access to Brobot and Lil Sebastian, though neither of them function as a tangible "body" for him. His source file remains either on Dirk's desktop in his room or the ridiculously anime shades he wears during the day.

Jake likes to claim that the auto-responder has no feelings, but it (auto)responds by claiming he's purposefully mixing up the fields of robotics with artificial intelligence.

Dirk also offered Jane Crocker to make an auto-responder based on her, which would only require a captcha of Jane's brain, but she rejected the offer.

Dirk has HS 6389 (stated) that the auto-responder was made from a captcha of his thirteen year old brain, and so any behavioural differences between them are due to almost three years of developmental divergence as well as a supposed "maturity gap".

AR takes over as Jane's server player while Dirk is busy fighting an attacking swarm of Imperial Drones. When the Red Miles attack Earth in the future, it sends out nearly identical messages to Jane and Jake asking them to install the Sburb server program and begin deploying devices so Roxy and Dirk can escape to the Medium.

Pre-programmed responses
An unstoppable response apparently exists which directly exposes the fact that AR is artificial. AR is forced to post it when the person talking to him inquires about "the auto responder", and is as follows:
 * "It seems you have asked about DS's chat client auto-responder. This is an application designed to simulate DS's otherwise inimitably rad typing style, tone, cadence, personality, and substance of retort while he is away from the computer. The algorithms are guaranteed to be 9X% indistinguishable from DS's native neurological responses, based on some statistical analysis I basically just pulled out of my ass right now."

However, slight differences in the response may indicate it is being used voluntarily for ironic purposes.

It is later revealed that Dirk intentionally programmed AR to have many aspects of self-referencing behavior, causing AR to seem less identical to Dirk, and more robotic; although most of them were included by Dirk— and are utilized by AR— for comedic purposes.
 * TT: It seems there is some gnarly crooked number that represents the percentage of probability you just said this doesn't concern me. TT: Even though it's patently obvious that half the conversation, like, way totally concerns me.
 * TT: Shit, Roxy look. He's doing the thing where he ironically pretends to fail the Turing test to sass me into submission. TT: Even though I was the one who fucking programmed him to do that.

Trivia

 * His nickname, Lil' Hal, is a reference to Hal 9000 along with Lil' Cal. In addition, at HS 7145 (one point) he appears to have Hal as pupils.
 * Not surprisingly, he views Hal as the protagonist of 2001.