Before the Big Bang
The Big Bang was the EXPANSION of space that created the universe as we know it.
What was before the big bang?
Do not confuse "what was" with "what happened". There is no way to know what happened before the big bang, but physicists have some theories on what existed before the expansion of space called "Big Bang":
Before the expansion, the entire universe was compressed into (nearly) infinitely small dimensions that were so small that the entire universe was subject to quantum mechanical uncertainty.
Most scientists now believe that we live in a finite expanding universe which has not existed forever, and that all the matter, energy and space in the universe was once squeezed into an infinitesimally small volume, which erupted in a cataclysmic "explosion" which has become known as the Big Bang.
New Study Reveals Dark Matter May Have Predated the Big Bang