Mace Windu deals the death blow in the Geonosian arena in Attack of the Clones. Mace Windu, using the lightsaber technique Vapaad.
On Geonosis. That's where a variety of battledroids are made. Plus it is the first planet to create the awesome super battledroids and star plans for the Death Star, i hope this answer has been...
He announced the beginning of the Clone Wars. Remember he said: "Begun the Clone War has."
PG