Designed to supplement Disneyland in Anaheim, California, which had opened in 1955, the complex was developed by Walt Disney in the 1960s. "The Florida Project", as it was known, was intended to present a distinct vision with its own diverse set of attractions. Walt Disney's original plans also called for the inclusion of an "Experimental Prototype Community of Tomorrow" (EPCOT), a planned community intended to serve as a testbed for new city-living innovations. Walt Disney died on December 15, 1966, during the initial planning of the complex. After his death, the company wrestled with the idea of whether to bring the Disney World project to fruition; however, Walt's older brother, Roy O. Disney, came out of retirement to make sure Walt's biggest dream was realized. Construction started in 1967, with the company instead building a resort similar to Disneyland, abandoning the experimental concepts for a planned community. The Magic Kingdom was the first theme park to open in the complex, in 1971, followed by Epcot (1982), Disney's Hollywood Studios (1989), and Disney's Animal Kingdom (1998). It was Roy who insisted the name of the entire complex be changed from Disney World to Walt Disney World, ensuring that people would remember that the project was Walt's dream.
Give me a brief history of the construction of Walt Disney World
Walt Disney World was designed as a theme park to supplement Disneyland.  It was conceived by Walt Disney in the 1960s and was known as the "The Florida Project".  Walt Disney originally envisioned including a planned community known as the "Experimental Prototype Community of Tomorrow" (EPCOT) which would be a planned community that would test city-living innovations.  As planning progressed, plans for EPCOT evolved to become just a theme park in the complex.  Walt Disney died in 1966 during planning and the company was torn whether to move forward with the project.  Walt Disney's brother, Roy Disney, came out of retirement to see the project successfully completed.  There are four theme parks in the complex.  The Magic Kingdom opened in 1971, followed by Epcot in 1982, Disney's Hollywood Studios in 1989, and Disney's Animal Kingdom in 1998.  Roy Disney insisted the name be changed to Walt Disney World from the original name of just Disney World to remind people that it was Walt's dream.