Clarence Abiathar Waldo (January 21, 1852 – October 1, 1926) was an American mathematician, author and educator, most famous, today, for the role he played in the Indiana Pi Bill affair.

[1] Born in Hammond, New York, Waldo married Abby Wright Allen (1856–?)

[2] A member of Sigma Xi and Phi Beta Kappa, he was tutor at the Department of Mathematics of Wesleyan University from 1877 to 1881.

[3] In 1888 Waldo published A manual of descriptive geometry, with numerous problems.

He achieved a modicum of fame that year when he explained to members of the Indiana State Senate why a bill that would redefine the value of pi and attempt to square the circle should not be adopted.