Which Dr. Seuss book features a character named Sam-I-Am?

The Dr. Seuss book featuring Sam-I-Am is 'Green Eggs and Ham'.

Published by Random House's Beginner Books imprint on August 12, 1960, 'Green Eggs and Ham' follows Sam-I-Am as he repeatedly urges an unnamed character to try the unusual dish. The reluctant character refuses in a series of increasingly elaborate settings—on a train, in a car, on a boat, and with a goat—before finally tasting the food and discovering that he likes it.

The book has an unusual origin story. Editor Bennett Cerf bet Theodor Seuss Geisel, writing as Dr. Seuss, that he could not create an engaging book using only 50 different words. Geisel accepted the challenge, and the finished book uses exactly 50 distinct words. That constraint helped produce its short sentences, strong rhythm, and memorable repetition.

Sam-I-Am is not the title character of 'The Cat in the Hat', 'Horton Hears a Who!', or 'How the Grinch Stole Christmas'. Those books feature different central characters and stories. The hyphenated spelling “Sam-I-Am” is part of the character's distinctive name and also supports the book's rhyme and meter.