In the first book, John Carter befriends the fearsome Woola and saves him from being killed by the Tharks, turning a terrifying monster into his loyal pet.
The Gods of Mars
In The Gods of Mars, upon finding himself returned to Barsoom and reunited with Tars Tarkas, John Carter's first moment of joy comes when Tarkas reveals to Carter that Dejah Thoris is still alive, thanks to John Carter's actions in the end of the previous book.
Tars Tarkas also gets one himself for the lengths he was willing to go to for his missing friend. John Carter had been missing from Barsoom for ten years, and yet Tars Tarkas never abandoned his search for him, even going so far as to journey to the River Iss, from where no one was allowed, at the time, to return.
The Warlord of Mars
At the end of the book, Phaidor saves John Carter and Dejah Thoris from the brutish Thurid.
The Chessmen of Mars
I-Gos, the creepy old taxidermist of Manator, ultimately proves to be a good guy who helps Gahan and Tara to defeat O-Tar.