Batman creator Bob Kane’s own copies of the Caped Crusader’s earliest appearances are going up for auction.

Online auction house ComicConnect is selling Kane’s file copies of Detective Comics Nos. 27 through 45 and Batman Nos. 1 through 3. The vendor declined to put an estimate on their value, saying such items rarely come up for sale.

However, a single copy of a first-edition Detective Comics No. 27 — the 1939 compilation in which Batman made his debut — has sold at auction for more than $1 million US.

The comics come from the collection of Hollywood screenwriter Bob Underwood.

Kane created Batman when he was a 19-year-old cartoonist for Detective Comics. The first comic series to star Batman debuted a year later, in the spring of 1940. Kane died in 1998 at age 83.