>>80109616Hellboy's main story is contained in about 15 trade paperbacks. When people just say Hellboy, they're referring to the entire run. What you're thinking of is all the spin-off series such as Abe Sapien, BPRD, Hellboy in Hell, BPRD Hell on Earth, Lobster Johnson, Witchfinder, or that new Frankenstein one which I haven't read but have heard good things.
My favorite individual arc/trade of Hellboy proper is Darkness Calls. That's the one where the Baba Yaga tries very very VERY hard to kill Hellboy.
I hope that suitably answers your question. Of course there's probably more Hellboy fans in this thread because the OP image is of Hellboy.