Even though Bert is a grumpy, he is still sometimes happy. He's yellow with a single eyebrow called a unibrow, and had a vertical striped shirt (compared to Ernie's which is horizontal). He looks like a banana.
Bert first appeared in the test episodes of Sesame Street in 1969, with his uni brow never moving, and a little more tame. Then later in the years starting in Season 3 of Sesame Street, Bert can move his uni brow up and down. Starting in 1997, he was funnier and nicer but still grumpy. Bert has known to be changed nine times.