Original: Though founded in 1887, under Jack Hyles' leadership from 1959 & ndash; 2001 it became one of the megachurches in the United States and during the 1970s had the highest Sunday school attendance of any church in the world.
Simplified: It was under Jack Hyles leadership from 1959-2001 that it became a megachurch, one of the first in the United States, with a steady weekly attendance of around 20,000.