The chronology has gotten a little complicated over the years after so many story arcs and spinoffs, prompting fans to piece things together for themselves. As a result, there are conflicting reading orders and interpretations of how one should approach the somewhat daunting "Mignola-verse."
Luckily, Dark Horse provided SYFY WIRE with the official timeline graphic, which you can check out below. The entire thing begins with a quick note from the comics publisher:
"Beginning with the publication of Hellboy: Seed of Destruction #1 in 1994, the world encapsulating Hellboy, Liz Sherman, Abe Sapien, and the Bureau for Paranormal Research and Defense has expanded to more than 70 volumes of unique stories. From ancient dragons to sea witches, demons in Hell and countless mythical monsters, Hellboy's adventures have grown for 25 years and counting."
Interestingly, the timeline begins not with Hellboy, but in the late 19th century, with the Witchfinder series that revolves around Edward Grey and his thwarting of the vampire known as Vladimir Giurescu. Hellboy (aka Anung Un Rama) doesn't enter the picture until 1944, when he is summoned to Earth by Rasputin and the Nazis as part of Project Ragna Rok.
Before he arrived, however, the violent vigilante, Lobster Johnson, was cleaning up crime during the Great Depression and into World War II until his untimely death during a Nazi-caused explosion in Europe. In 1952, Hellboy became an honorary member of the human race and began fighting the occult on behalf of the B.R.P.D.
The timeline goes all the way up to 2017, the year in which Abe Sapien and Hellboy both rejoined the Bureau and set off to find a mysterious cult leader. Respective histories for Liz Sherman, Johann Kraus, Raimund Dietsel, Kate Corrigan, Benjamin Daimio, Nimue the Blood Queen, and Roger the homonculus are also mentioned.
In the upcoming R-rated Hellboy reboot movie (out April 12) from directed Neil Marshall, we'll get to see the cinematic debuts of Nimue (Milla Jovovich) and Lobster Johnson (Thomas Haden Church). Hellboy (David Harbour), Sapien (unconfirmed for the film), and Professor Bruttenholm (Ian McShane) were already portrayed by Ron Perlman, Doug Jones, and John Hurt in two previous Guillermo del Toro adaptations.