What was the first Hanna-Barbera cartoon?

"The Ruff and Reddy Show" (also known as Ruff and Reddy) is an American animated television series and the first made by Hanna-Barbera Productions for NBC. The series follows the adventures of Ruff, a smart and steadfast cat and Reddy, a good-natured and brave (but not overly bright) dog and also was presented by Screen Gems, the television arm of Columbia Pictures (now Sony Pictures Television). It premiered in December 1957 and ran for fifty episodes until April 1960, comprising three seasons.

Hanna and Barbera created the series as the first of their fledgling television operation, first named H-B Enterprises. The "buddy" theme had previously been explored in their "Tom and Jerry" theatrical shorts, but unlike "Tom and Jerry", "Ruff and Reddy" are not adversaries, but housemates and best friends. The series is notable as one of the earliest original animated television programs, and a pioneering use of limited animation techniques.