I'm running my players through the Emergence storyline and we're up to "A Blast from the Past" where, on page 51, it says

"someone else has been tracking Shalbermat and decides to help the runners: an accomplished hacker using the handle Lucifer. Somehow Lucifer knows of Shalbermat’s true identity and is out to take the scientist down."

Now is this Lucifer the light spirit from The Lucifer Deck, the Immortal elf Leonardo using his old handle, Renny from the VR1 short story using his old teacher's handle as an homage or, Ghost forbid, something else like Lucifer didn't really die or Green Lucifer from the Ancients for some reason?

I can see arguments for all of the above, but is there any official call from on high for this one?

Well, the most likely explanation is he's just an homonym, because the handle is cool and project an image that more than a few people in this kind of job can find desirable...

Well, the Halberstein connection would certainly point to somebody involved with him previously. Renni is out however, one of Ancient History's unpublished drafts says Renni goes by the handle Icarus now. Of course the fact that he both was involved in writing Emergence (IIRC) and wrote a throwback to Virtual Realities also points to somebody involved with Doc H.

...or it's just some random guy who thought Lucifer is a cool name, either b/c it's sooo grimdark evil, or because the rebellious bringer of enlightenment is a quite fitting name for crypto-anarchists

I was going with the Renni angle myself, as his teacher's name was Lucifer (although I'm guessing you already knew that).

I would guess it's an AI who had some tie to one of the TMs, or merely thought of them as kindred spirits considering that AIs were going through similar at that time. There's an indication of this when in the fluff piece opening the chapter after they all break out, a mysterious party comes to one of the escaped "patients" (think his name was Leonardo) telling him not to become what the media was portraying them as, and the TM didn't recognize who it was. Maybe it was another TM, maybe it was a sprite or a paragon, but my guess is on it having been an AI, foreshadowing what was to come out of that particular Pandora's Box of a year.

I'm leaning away from the anonymous hacker with a cool handle angle. It strikes me that the good folks who sat down and wrote that sentence probably had more in mind than randomly suggesting a deus ex to come in and help your runners, and then let that dangling plot thread fade into nothingness like yesterday's jam.
I've no doubt it's possible, but this is Shadowrun; a game with such an extensive history and back story that the toss out of one name has me wondering which Machiavellian scheme is being run.

Now the Renni angle makes a bit of sense because Dr. Halberstam's first reference was in the short story Virtual Realities so it might be a nice tie in with his last reference and Mr. Derie(of Ancient Files) both worked on Emergence and sings the praises of VR1, as well all should.
However, why not just go by Icarus. Those ideas also leave the idea that the Lucifer of the VR1 story didn't really die, but is floating around Ghost in the Machine style, but I don't know if I like the idea of my favorite Shadowrun story being post written by me without a blessing from on high.

If it's an AI, then it's probably the light spirit from "The Lucifer Deck." Much bemoaned, I know, but still a part of the universe and with it's own pleasantness. Besides, were I to write up stats for it, I'd probably use the AI rules.

Let's not write off Leonardo, though. An immortal elf with otaku abilities sans datajack before going sans datajack was cool. A TM looking at someone with the Pattern of the Matrix would be equally unrecognizable as any AI if he wanted to be. Not to mention the fact that Leo has had his finger in every inch of the Matrix pie since it's inception, so leaving him out of this might be remiss.

I'd just like to know if there is any word from on high so I know how to play him.

I actually think AH mentioned it was a deliberate shout-out. Renny makes another appearance in Unwired, IIRC.

Just got an e-mail from AH. While he didn't write that bit of the book, he seems to recall it was supposed to be the original Lucifer from VR1.
Now my players don't have to make a deal with an immortal elf.
Thanks one and all.