So, Dorothy picked up another pet on her vacation: a white kitten she called Eureka. Baum never tells us, though, if Dorothy found Eureka in Australia or San Francisco. Personally, I find the idea of Dorothy bringing a cat from another country to be a little implausible and lean towards the idea that she adopted Eureka shortly before Uncle Henry went on to Hugson's Ranch alone.
"Canary-birds?" he asked.
"Oh no; it's just Eureka, my kitten. I thought that was the best way to carry her."
The boy nodded.
"Eureka's a funny name for a cat," he remarked.
"I named my kitten that because I found it," she explained. "Uncle Henry says 'Eureka' means 'I have found it.'"
It is curious, though, that Dorothy arrives with an animal companion each time she visits Oz: she first arrives with Toto in The Wonderful Wizard of Oz, then with Billina in Ozma of Oz, and then Eureka in Dorothy and the Wizard in Oz. Toto accompanies her again (Baum notes in the introduction of Dorothy and the Wizard in Oz that readers wanted him to bring the little dog back) in the next two books.
Eureka doesn't really appear properly until Dorothy, Zeb and Jim arrive in the Land of the Mangaboos. Zeb notes right away that she is pink. Dorothy notes that the colored suns of the Land of the Mangaboos must be to blame because Eureka is a white cat. (Neill depicts Eureka as such consistently in his illustrations for the book.)
But most memorably of all, Eureka craves to eat one of the Wizard's tiny piglets throughout the book. She is repeatedly warned that she will not be allowed to do so, Jim even threatening to eat her if she does so. Baum finally gives her desire a payoff late in the book. The Wizard presented Ozma with one of the piglets as a gift, and she gave it an emerald collar and kept it in her bedroom. But one day when she asked Jellia to bring it to her, Jellia couldn't find it, but she saw Eureka leave.
Everyone believes that Eureka has eaten the piglet, but she refuses to confess. So Ozma has Eureka put on trial, defended by the Tin Woodman. Knowing that Eureka will likely be found guilty which will make Dorothy unhappy, the Wizard decides to offer another piglet to be revealed as the missing piglet. All goes exactly as he expected in a comic courtroom scene, and the Tin Woodman offers the new piglet after Eureka is deemed guilty.
Then the crowd cheered lustily and Dorothy hugged the kitten in her arms and told her how delighted she was to know that she was innocent.However, for attempting the crime, Eureka is not held in the best graces of the people of Oz and is confined to Dorothy's room. She prompts Dorothy to think about going back home to Kansas.
"But why didn't you tell us at first?" she asked.
"It would have spoiled the fun," replied the kitten, yawning.
Baum doesn't mention Eureka again until The Patchwork Girl of Oz. The Shaggy Man says that Dorothy has a pink kitten with blue eyes named Eureka. (Eric Shanower had Eureka mention that she came to Oz along with the rest of Dorothy's family in his The Secret Island of Oz, while his comic book adaptation of The Emerald City of Oz has Toto and Eureka both accompany Dorothy to her bedroom when she signs for Ozma to bring her to Oz.) The curious thing is that he says that she's a favorite at the palace and that if Bungle the Glass Cat becomes Eureka's friend, she has no fear of being broken.
Curiously, in Glinda of Oz, Dorothy refers to Eureka as her purple kitten. Most fans ignore this, and there are a number of fan-written tales that explain how Eureka went from white—a fairly normal color for cats—to pink, a fairly unusual color for cats. A few tackle the purple issue as well, but generally when Eureka does turn up in new tales, she is pink.
Perhaps Baum vividly remembered Zeb's first glimpse of Eureka, or a fan who remembered it well asked what became of Eureka and mistakenly called her the pink kitten. And so, Baum threw in the few lines of the Shaggy Man's dialogue in The Patchwork Girl of Oz to reassure readers that Dorothy's cat was in Oz with her as well as her more famous dog Toto. It is rather disappointing that little documentation of the creation of the Oz series survives and so we have no idea if some of these were simply Baum mis-remembering his own work (and considering Baum's extensive output, you can't exactly expect him to keep everything on his mind) or if he was trying to please his reader's specific requests.
Eureka is loyal to her owner and the friends she does make, but at the end of the day, she's a cat. While her desire to eat a piglet in Dorothy and the Wizard in Oz is a rather nasty part of her character, she is simply responding to her natural instinct of hunting. She is smug, observant and self-centered, personalities many cat owners imagine in their pets. It is a fact that the Baum family had at least one cat: one of Baum's sons was punished by Maud for dunking a cat in a rain barrel by being treated in the same manner. Baum mentioned on an anniversary card that one of the few times Maud was in tears was because the cat died. Finally, in a photograph of his Chicago home, one of Baum's sons is seen holding a cat.
While Eureka may have been mentioned in later books in the Famous Forty, she never plays an important role again in them.
Eureka is another example of Baum using the characteristics of an animal and working it into a character. It wasn't enough to say that a cat was speaking or doing things, readers had to believe that Eureka actually was a cat, and when it came to this one, Baum really excelled.