What is the name of Arthur's third-grade teacher?

Arthur's third-grade teacher is Mr. Ratburn.

Nigel Ratburn teaches Arthur and his classmates at Lakewood Elementary School. He is known for assigning demanding homework, insisting on careful preparation, and expecting students to take school seriously. Despite his strict classroom style, the students respect him and often show that they value his guidance.

The character appears in both the books and the television series. His name is sometimes shortened to Mr. Ratburn, while early material and credits may identify him as Emil Ratburn. Arthur remains in third grade for much of the series, and Ratburn later teaches the class in fourth grade as well.

A common mix-up is confusing Ratburn with Mr. Haney, Lakewood's principal, or with substitute teachers such as Miss Sweetwater. Ratburn's personality was partly inspired by Marc Brown's own middle-school algebra teacher, although the fictional character teaches elementary school.