Seven authors and a dozen comic creators and artists were also announced. Brandenburg said more celebrity appearances are being finalized.
Here, in alphabetical order, are the 13 celebrity guests named so far:
John Barrowman • who played the omnisexual Capt. Jack Harkness on "Doctor Who" and "Torchwood," and plays the calculating Malcolm Merlyn on "Arrow."
Corbin Bernsen • whose credits include "L.A. Law," "Major League" and "Psych."
Will Friedle • who played best pal Eric Matthews on "Boy Meets World," and has a long voice-acting career in animation.
Sean Gunn • who played Kraglin, one of the Ravagers, in the "Guardians of the Galaxy" movies, and the nerdy Kirk in "Gilmore Girls."
Val Kilmer • known for playing Batman in "Batman Forever," Tom Cruise's flyboy rival in "Top Gun," and Doc Holliday in "Tombstone." (Previously announced.)
Christopher Lloyd • who played Doc Brown in the "Back to the Future" trilogy, as well as roles in "The Addams Family," "Who Framed Roger Rabbit" and many others.
Eoin Macken • who played Sir Gwaine on Syfy's series "Merlin."
Michael Rooker • who plays the blue-headed Yondu in "Guardians of the Galaxy Vol. 2," and played the combative Merle on "The Walking Dead." (Previously announced.)
Michael Rosenbaum • who played the villain Lex Luthor on "Smallville" and a phony clergyman on TV Land's "Impastor." (Previously announced.)
Jewel Staite • who played the plucky engineer Kaylee Frye on Joss Whedon's space opera "Firefly," and had roles on "Stargate: Atlantis" and "The Killing."
Catherine Tate • the British comic who played companion Donna Noble on "Doctor Who," and joined the cast of "The Office" as the sharp-tongued Nellie.
Will Wheaton • who played young Wesley Crusher on "Star Trek: The Next Generation," and more recently has played himself on "The Big Bang Theory."