Ernest the Grouch is Oscar's brother. He looks like Oscar, but with bushy black eyebrows and a scuzzy green mustache.
Ernest first appeared on Sesame Street in Season 8, paying his brother a visit in Episode 0954. Oscar decorates his trash can, dresses neatly, and pretends to be nice as a way of getting even with Ernest, who was the favorite kid in their family. Ernest decides to play along and attempts to act nicer than Oscar. The two continue to outdo each other, but Luis and Maria hatch a plan to return them to their grouchy selves. Mr. Hooper makes a concoction of peanut butter, ketchup, pickles, and sauerkraut, and when offered the meal, the two Grouches instantly start fighting over it.
Ernest payed another visit in Episode 1688, where it is established that he lives in Chicago and fills a similar role to Oscar as the street grouch; the same street Mr. Hooper's brother Arnold Hooper lives on. Ernest appeared again in Episode 2720; which itself was a remake of Episode 0954, but with Gordon and Gina as the main human cast members.
Ernest also planned a visit in the 1987 book Oh, Brother! which also had Oscar planning on being nice. However, after all of Oscar's planning, Ernest calls to inform him that he's canceling plans to visit, but after Oscar messes things up again, decides to come over after all.
In his first appearance, Ernest was recycled from a spare Oscar puppet, and wore no clothing. The redesigned Ernest wore a white collar and blue bow tie.