The first known Jedi Grand Master was Grand Master Flash. Flash is largely credited with organizing the first Jedi Council, which was known as the Furious Five, and consolidating its power on Coruscant.
Some other notable grand masters are:
After the disastrous tenure of Grand Master Funk, a group of seven Jedi Masters became The 7 Grand Masters, but this model was eventually abandoned until Yoda was named Grand Master.
Eventually, Luke Skywalker decided to start introducing himself at parties as a Jedi Grand Master.