In 1990, Bart quickly became one of the most popular characters on television in what was termed "Bartmania". He became the most prevalent "Simpsons" character on memorabilia, such as T-shirts. In the early 1990s, millions of T-shirts featuring Bart were sold; as many as one million were sold on some days. Believing Bart to be a bad role model, several American public schools banned T-shirts featuring Bart next to captions such as "I'm Bart Simpson. Who the hell are you?" and "Underachiever ('And proud of it, man!')". "The Simpsons" merchandise sold well and generated $2 billion in revenue during the first 14 months of sales. The success of Bart Simpson merchandise inspired an entire line of black market counterfeit items, especially T-shirts. Some featured Bart announcing various slogans, others depicted redesigns of the character, including "Teenage Mutant Ninja Bart, Air Simpson Bart, [and RastaBart". Matt Groening generally did not object to bootleg merchandise, but took exception to a series of "Nazi Bart" shirts which depicted Bart in Nazi uniform or as a white power skinhead. 20th Century Fox sued the creator of the shirts, who eventually agreed to stop making them.