Pizza Hut introduced stuffed crust pizza in 1995. The chain launched the product in the United States on March 25, 1995, with a ring of mozzarella enclosed inside the outer edge of the crust rather than placed only on top.
The idea is credited to Pizza Hut food developer Patty Scheibmeir, and the launch received major publicity through a television commercial featuring Donald and Ivana Trump. The novelty was not simply extra cheese: it changed the way diners ate the pizza, encouraging them to save the crust for a cheese-filled final bite.
The product became one of Pizza Hut's most popular lines by the end of that year. The exact launch date is sometimes listed as March 26 in Pizza Hut-related summaries, but both dates fall within 1995, which is the answer required by the question.
Pizza Hut popularized the style, although it was not the first person to claim the underlying concept. Anthony Mongiello's family had patented a stuffed pizza shell in 1987, leading to a later lawsuit that Pizza Hut ultimately won.