When Ruth Plumly Thompson took over the writing of the Oz series with The Royal Book of Oz, she immediately began adding her own creations to the already pretty full roster of recurring characters. Her first Oz book introduced not only Sir Hokus of Pokes, but also the Comfortable Camel and Doubtful Dromedary, known as Camy and Doubty for short. The two camels come from the desert domain of Samandra, one of the few parts of Oz where animals are unable to speak. While in a caravan, a sandstorm blows the two of them to the main part of Oz, where they're surprised to learn they can converse with humans. Camy takes an immediate liking to Sir Hokus, and denotes the knight as his new Karwan Bashi, a term for the leader of a caravan that I think might actually come from Persia. The personalities of the camels aren't all that deep, with Camy being a perpetual optimist and doting companion, while Doubty is a pessimist who doubts everything. The two come to live in the Emerald City, where they occasionally show up to make comments, but the next major role for one of them isn't until Yellow Knight. In this book, we learn that the Sultan of Samandra had stocked the magic dates needed to restore the kingdoms of Corumbia and Corabia in Camy's saddle sacks, and after a ten-year search his seer Chinda has discovered the camel in the Emerald City. The Sultan temporarily retrieves Camy, only to find out that the dates are gone from the sack. At the end of this story, Camy ends up settling in Corumbia with Sir Hokus, but Doubty doesn't. Wishing Horse confirms that the two of them are living in separate places, and I found it a bit odd for Thompson to break up the duo.
One oddity of John R. Neill's drawings of the two is that, as suggested here, he might not have known what a dromedary was. The term properly refers to a one-humped camel (the two-humped is a Bactrian), but it was apparently once common for people to confuse the two.
Thompson eventually brought in another camel protagonist, Humpty, in her Enchanted Island. He doesn't come from Samandra, but rather from Hah Hoh Humbad in the Munchkin Country. He was the favorite steed of the Shah of that place, but he was stolen by robbers and sold to a circus in the Outside World. David Perry finds him at the circus, and with some help from a magic wishing button that his grandmother attached to his shirt, the two of them journey to Oz. While he originally plans to return to Humbad, Humpty ends up settling with the shepherd Malacca Malloo in the Kingdom of Kapurta.