This is the giant robber fly Promachus bastardii. That name seems to mean "the bastard's champion." I understand the champion part, at least; these are carnivorous flies that take large prey. They're big, hairy, aggressive, and loud. In close-up they're unexpectedly cute, with their bulging eyes and blond facial hair.
From certain angles, they remind me of terriers.
Males have a white tag at the end of their abdomens, rather like a lobster's tail fan.
Females have a tapering abdomen and run larger.
These guys can be challenging to stalk because of their good eyesight, but sometimes they obviously see me and just aren't impressed. This one rode around on my camera bag and ignored the lens I was sticking in its face.