Short answers, pulled from the story.
Dave Arneson wrote the Blackmoor supplement, with a foreword by Gary Gygax. It carries the TSR product designation 2004 and was published in 1975 as Supplement II to the original Dungeons and Dragons rulebooks.
The Blackmoor supplement introduced the assassin, a sub-class of the thief, and the monk, a monastic martial arts sub-class of the cleric intended to be a hybrid of the fighter and thief classes. A Sage character was also introduced but reclassified as a Non-Player Character type by the editor.
The Temple of the Frog is the first role-playing game adventure ever published, included in the original Blackmoor supplement. It was later revised and expanded and republished as a standalone product under the designation DA2 Temple of the Frog.
TSR, Inc. published the Blackmoor supplement in 1975 as a sixty-page digest-sized book. Gary Gygax had announced in March 1975 that Arneson was completing a final draft, and the product had been advertised in The Strategic Review.
The booklet passed through two editors, Brian Blume and Tim Kask, and was temporarily misplaced during production. The final edit was completed hastily in only a few weeks.
Blackmoor was reprinted on the 19th of November 2013 as part of a premium deluxe reprint of the original White Box, packaged in an oaken box. The reprint included all four original supplements and gave each new cover art while preserving the original interior content.