The Sandman comic series was set in the DC Universe, however, the adaptation sets it apart with DC comics being a thing that exists in the universe as noticed by various superhero toys and the fact that an episode of Static Shock can be seen on one television. However, The Sandman features a wide variety of colorful characters that went on to lead their own comic series like Death, Merv Pumpkinhead, and Joanna Constantine who is a reworking of the classic DC character John Constantine. The Sandman series was so popular it led to multiple spinoffs that could form a franchise for Netflix that is as rich and detailed as the Harry Potter series.
In an interview with Variety, Gaiman was asked about potential spinoffs for The Sandman. The two characters Gaiman immediately mentioned was Death (Kirby Howell-Baptiste) and Johanna Constantine (Jenna Coleman). Gaiman did not confirm any spinoffs were in development but did say they could use the Death comics as a basis and would love to see Johanna battling various demons. Gaiman said:
"We also have the 'Death' books. It might be great to go off and do one of those as a sideline, in addition to which, anybody who has seen 'Sandman' Episode 3 has sidled over to us at some point or other in the last six months and said, 'Do you think there’s any possibility that we could do a Johanna Constantine show with Jenna Coleman?' And, oh my God, she’s a star and you just want to see her going through battling demons and destroying other people’s lives. So that’s in there, too. We can keep going on this for a long time to come."
Gaiman wrote two Death comics, Death: The High Cost of Living in 1993 and Death: The Time of Your Life in 1996, both of which could easily form the basis of a spinoff series. The Johanna Constantine comment, in particular, is interesting as HBO Max is currently developing a Constantine series that despite recent cancelations by Warner Bros. Discovery still seems to be moving along. Another series in development at HBO Max is Dead Boy Detectives, which are also characters that originated in The Sandman comics, although it will not be connected to The Sandman series.
One notable character Gaiman did not mention is Lucifer (Gwendoline Christie), who did get their own spinoff comic which ran from 2000 to 2006 and was loosely adapted into the hit television series starring Tom Ellis. That series made many changes to the source material and with how The Sandman season 1 concludes, it seemed like a possibility the series could lay the groundwork for a more faithful adaptation of the Lucifer comics. While Netflix has not yet greenlit The Sandman for season 2, the streamer has plenty of source material to draw from that could run for years.