Ernest T. is an ignorant and rowdy mountain man with a penchant for troublemaking, which wreaks havoc on the otherwise sedate town of Mayberry. Once in a while, he appears in town with his trademark greeting, "Howdy do to you and you. It's me, it's me, it's Ernest T.!" This invariably means trouble for Sheriff Taylor and Deputy Barney Fife. Ernest T. is a wild, belligerent hillbilly with a scruffy, unkempt appearance, a maniacal laugh, and often speaks in rhyme. When threatened with the law, Ernest T. is adept at eluding Sheriff Taylor and Deputy Fife. He taunts the two lawmen with his famous catchphrase, "You ain't seen the las' of Ernest T. Bass!" Ernest T. loves breaking windows with rocks and prides himself on being "the best rock thrower in the county." He is notoriously importunate with the women he desires, and regularly uses this tactic to get their attention. He also tries to impress people by informing them that he is saving up for a gold tooth. He once boasted that he had lifted a mule onto his shoulders and "tote' her five miles to the doctor," an impressive feat of strength (if true).
His behavior is summed up succinctly (and repeatedly) by Deputy Fife: "He's a nut!"
Despite his checkered past and his generally rude ways, Andy more than once takes Ernest T. under his wing and tries to educate him in the ways of the world. One time, Andy tries to turn Ernest T. into a presentable gentleman. He takes him to Mrs. Wiley's party and tries to pass him off as his cousin, Mr. Gosage. This episode is a comedic parody of My Fair Lady.
In his first appearance (Episode #94, "Mountain Wedding"), Ernest T. has his mind set on marrying Briscoe Darling's daughter Charlene, despite the fact that she is already married to Dud Wash. He breaks the Darlings' window in the middle of the night, and then attempts to serenade Charlene by performing a sort of spoken-word song called "Old Aunt Mariah," accompanied by drumming a gas can, which he "tuned" by tightening and loosening the cap. The family then decides to conduct a faked wedding, to which Ernest T. reacts by devising a nefarious plan to steal the bride, only to discover that it was Barney in disguise.
In Episode #133, "The Education of Ernest T. Bass", he tries to impress his love interest Ramona (whom he always calls "Romena") by getting an education. It is revealed that he cannot read or write, except for a few posted signs around town and in the hills. (This is somewhat contradictory to earlier episodes, in which he often throws rocks with written notes attached.) Ernest T. attends Helen Crump's elementary school class, where he quickly becomes a nuisance. After she smacks him with a ruler for being disruptive, Ernest T. begins to bond with Miss Crump, calling her his "mother figure," in his signature drawl. Fed up, Helen decides—on Andy's advice—to graduate Ernest T., despite his insufficient education. She gives him his "diploma," which is simply a certificate stating that he knows some arithmetic, can read and write some words, and knows the boundaries of the United States. In a touching ceremony, she announces that Ernest T. Bass has received his diploma "for learning...for learning".
Ernest T. Bass' final appearance was in Episode #162, "Malcolm at the Crossroads." He is fired as crossing guard in favor of Malcolm Merriweather, played by Bernard Fox. When Bass first saw Malcolm on the job, he said, "Looks like a octopus!"
Despite only appearing in five episodes during the series' entire run, Ernest T. Bass is one of The Andy Griffith Show's best remembered characters, and remains a fan favorite. Morris, along with Griffith, Knotts, and many other cast members reprised his role in the 1986 TV movie Return to Mayberry.
Ernest T. Bass' rock-throwing exploits are commemorated in the Natural Science sections of some museums and universities in the U.S. with "Ernest T. Bass Day," in which people who have stones they are unable to identify are encouraged to bring them in for inspection. This usually takes place on April 1, when Bass is believed to have celebrated his birthday on the show.