Toto
Toto is the small dog companion of Dorothy Gale in L. Frank Baum's 1900 novel The Wonderful Wizard of Oz. Baum described Toto as "a little black dog, with long, silky hair and small, black eyes that twinkled merrily on either side of his funny, wee nose" — illustrations by W. W. Denslow rendered him as a Cairn Terrier-like creature, but the breed is never specified in the text. The 1939 MGM film The Wizard of Oz cast a female brindle Cairn Terrier named Terry as Toto, and Cairn Terriers have been popularly associated with the role ever since.
Terry the dog was paid $125 per week for the film — substantially more than many of the human Munchkin actors. After the film's release, Terry's owner officially renamed her Toto. The film's iconic "Toto, I've a feeling we're not in Kansas anymore" line, spoken by Judy Garland, has become a cultural touchstone independent of the film itself, often used to describe any feeling of dislocation or unfamiliar territory.
Across the Oz franchise — 14 Baum novels, dozens of subsequent novels by other authors, multiple films, and stage adaptations — Toto remains one of the most-portrayed fictional dogs in American media history. The Cairn Terrier breed saw a major popularity surge after the 1939 film and remains popular in part because of the association.
Naming takeaway
Toto is the canonical Cairn Terrier name, plus the default small-black-dog reference for Wizard of Oz fans. Two clean syllables, soft T opening, projects easily. Best fits Cairn Terrier (where the reference is most direct), Norwich Terrier, Yorkshire Terrier, and any small dark-coated terrier or terrier mix. Ranks in the top 200 dog names in English-speaking markets, with strong demographic concentration in 1930s-revival aesthetic.
Cross-referenced against the Wikipedia entry. Where text is paraphrased from Wikipedia, the original is licensed under CC-BY-SA 3.0; image licenses are noted per image above.