Followup to this old question Did Edgar Rice Burroughs ever write a fictional work (novel, tale, etc..) depicting Tarzan on Mars? that recently reappeared. (also the source of the image)
At the left and right of the bookplate characters 1 from ERB's fiction are depicted. Who are they?
1 See answer to linked question for an image of a letter from ERB stating that the depicted individuals are characters from his fiction.
Unfortunately, Burroughs didn't describe many of his characters well, so it is difficult to identify them absolutely, with few exceptions.
Partial answer:
Besides Tarzan, the easiest to identify is Kala, the ape who raised Tarzan. She is portrayed holding his legs, and is the only non-Tarzan explicitly identified in a letter from Burroughs linked in an answer here, to the question that inspired this question
The bearded man wearing a Russian star and sickle (top row, middle, to the left of Tarzan) is probably the nemesis ("sapristi") Nicholas Rokoff or possibly his henchman Alexis Paulvitch (who is described has having a beard) from The Return of Tarzan as well as several other novels.
The man with monocle and top-hat (top row, closest to Tarzan) could be William Cecil Clayton (Lord Greystoke), the person who inherits the Earldom and associated property upon the assumed death of Tarzan's parents without heir. These titles Tarzan inherits upon his reaching civilization. is Professor Archimedes Q. Porter he is described as:
an elderly man, with white hair and large rimmed spectacles. His slightly stooped shoulders were draped in an ill-fitting, though immaculate, frock coat, and a shiny silk hat
The woman's head below the Russian (middle row, middle head to the left of Tarzan) is almost certainly the famous Jane Porter, Tarzan's wife, but could equally be Dejah Thoris from the John Carter/Barsoom series of books.
The head behind Tarzan (top) with the kepi is probably Paul d'Arnot (Frenchman), who appears in Tarzan of the Apes and The Return of Tarzan. d'Arnot "rescues" Tarzan from the jungle and gets him restored as Earl Greystoke. The kepi is a stereotypical French military hat. There's another military figure on the left (top, face cut-off), but I don't know who that would be. Someone may be able to identify the gorget to get it to a branch of military and nation. It may be that this is either one of the Germans that oppose Tarzan in Tarzan the Terrible, and Tarzan the Untamed, or it could be Jack/Korak, Tarzan and Jane's son, who fights for the British Army on the Argonne Front (as mentioned in Tarzan the Terrible).
The stereotypical African figure behind Tarzan (middle, below man in hat only seen partially) is probably meant to represent the Waziri, who Tarzan becomes chieftain of The head could also represent one of the Waziri, Busili, who is the first Waziri Tarzan befriends. The Waziri feature in a number of the novels, particularly Tarzan and the Jewels of Opar and The Return of Tarzan.
These next ones are guesses. Anyone who wants to chime in, please do so:
The head with the helmet on the bottom row, closest to Tarzan, might well be one of the Martian characters from the Barsoom/John Carter series. This might be Kantos Kan, as he is the most prominent Martian figure in the series.
Equally, the head with the tonsure could be a Thern from the Barsoom series, as these are portrayed as the main villains in this series and are called "Holy Therns" being the religious leaders of Barsoom. However, the Therns are described as bald and wig-wearing.
I also wonder if the head directly above Kala is John Carter, wearing the neckerchief and stetson of his mining/prospecting character, as we see him at the start of A Princess of Mars.
