Toto plays a key role in The Wizard of Oz. L. Frank Baum emphasizes the dreariness of Dorothy's life in Kansas and describes Toto as the only thing that brings her joy. Toto is the focus of the conflict between Dorothy and Miss Gulch and the reason Dorothy is caught in the storm that takes her to Oz. In Oz, Toto is the one who reveals the Wizard of Oz to be a fraud, but he also causes Dorothy to miss her return balloon flight. Given the prominent role Toto plays in the story, it is surprising that Henry Littlefield does not include Toto in his analysis of the parallels between the Populist movement and The Wonderful Wizard of Oz. Littlefield makes only one passing reference to Dorothy's dog in his article "The Wizard of Oz: Parable on Populism".  In his 1971 book The Winning of the Midwest, Richard Jensen filled that void by pointing out that the name Toto was likely a reference to prohibitionists (that is, "teetotalers") who were important allies of the Populists in the free silver coalition.  Michael Patrick Hearn, who argues that Baum did not intend to write a Populist allegory, points out that people on the Great Plains often had pets for companions. Toto was a popular name for dogs in the 19th century and was also a popular nickname for young boys in France at that time. 
Most of the spiritual interpretations of The Wizard of Oz see Toto only in terms of his relationship to Dorothy. In his Zen Buddhist interpretation of The Wizard of Oz, Joey Green points out that Toto is the only one who loves Dorothy unconditionally, but Dorothy invites trouble by allowing Toto to run through Miss Gulch's garden in an effort to get Aunt Em and Uncle Henry to take notice of her. Darren John Main in his New Age interpretation of The Wizard of Oz argues that Toto is an extension of Dorothy's character. Toto represents the creative part of the soul that may lead us into trouble but also uncovers important lessons. As he puts it, "Toto has one major function—to rock Dorothy's world."  In his Christian interpretation, Samuel Bousky suggests that Toto represents something more profound. He argues that Dorothy represents the spirit of humankind while Toto represents the physical body. Toto comes from the Latin Totum, which means whole. Together these two characters represent the whole of humanity. 
Hearn speculates that Baum intended for Toto to be a mongrel. W.W. Denslow, the original illustrator for The Wonderful Wizard of Oz, drew Toto as a terrier. When casting the 1939 movie, MGM took pains to find a dog that looked like Denslow's drawings. A cairn terrier named Terry was chosen to play the part of Toto.  And if you think Toto was universally loved, think again. In his book on The Wizard of Oz Salman Rushdie confesses, "I couldn't stand Toto. I still can't." He refers to Toto as "that yapping hairpiece of a creature, that meddlesome rug! (I should point out that I felt this way about Toto even when I still had hair of my own.)"