Peter Norman, an Aussie. Actually it wasn't his gloves, one of them (Smith or Carlos) had forgotten to bring his so Norman suggested they used one each from the single pair.You’ll notice one glove is on the right hand and one glove is on the left hand.
The white athlete leant the others his gloves for that shot.
He was apparently roundly castigated in Australia for this, and was ostracised. However Smith and Carlos never forgot, and when he died one of them was a pallbearer at his funeral.
EDIT: Just checked, and both were pallbearers.