The Entertainment District used to be almost completely industrial until about the 1970s. After the completion of the CN Tower in '76, more and more entertainment businesses started moving in. The '80s and '90s saw an influx of night clubs and theatres which is what the district is now known for.
Oh, and the Skydome, yeah, that thing... because there's always next year.
Since the 200s there has been a condo boom spiking the population of the district from 750 people well into the ten thousands.