Dejah Thoris and John Carter originated in the works of Edgar Rice Burroughs, specifically the Barsoom novels spinning off from A Princess of Mars. Both characters were introduced in this book, serialised in 1912 and released in collected form in 1917; as such, they are in the public domain. However, the same is not true of handmaidens Brin and Loo, who originated in a modern continuation, the 2012 comic miniseries Dejah Thoris and the White Apes of Mars.
