"We call this the Mainframe. Fifty three separate realities arranged in a thermodynamically stable grid. Indigo Prime® is located in a hypothetical nullzone outside the Mainframe. Every event in time and space transects this point. As you can imagine, it puts us right at the heart of things. We also carry out routine maintenance in all parallels. Make sure everything runs smoothly... quantum laws, entropy, flood, famine and pestilence — that sort of thing."
Indigo Prime is a series by John Smith about a powerful and esoteric organisation of the same name that polices reality itself and has the ability to warp time, space and human minds as it sees fit. Elements of it had previously appeared in the Fervent and Lobe story in progs 642-649, and in a Future Shock in prog 490. Two of its agents also popped up in a Tyranny Rex story before it finally débuted under its own title in 2000 AD prog 678. If this sounds complicated, that's because it is. So are the stories.
To be an Indigo Prime agent, you must (a) have a genetic component called the Rembrandt Index™, found in about one in twelve million people, and (b) be dead. After death agents are installed in new bodies and trained in a discipline. Sceneshifters alter physical matter, seamsters sew stitches in time, and imagineers alter people's minds (not through eloquence, but via more direct methods like dream-shaping and tweaking the unconsciousness, which are a lot more fun). The multiverse they police is sometimes called the 'Smithiverse' (by Squaxx dek Thargo, not by the characters themselves), and its artists have included Edmund Bagwell, Lee Carter, Mike Hadley and Chris Weston.
Indigo Prime took a bit of a break from 2000 AD's pages after 1992, but came back somewhat unexpectedly in the final panel of the 2008 series Dead Eyes. Since then, they have returned to business as unusual.
Parts of this series were reprinted in the Quality title Time Killers.