First powered, sustained flight. I don’t see how a glider fits into powered.
If memory serves, Orville Wright’s last flight was with Howard Hughes.
If prior to the Wright Brothers' flight someone had produced a glider which was sufficiently efficient that it could remain aloft indefinitely in the presence of naturally-occurring thermals or other updrafts, I would have regarded such an accomplishment as being no less significant than that of the Wright Brothers. What was significant about the Wright Brothers was not that their plane was powered, but rather that it could remain aloft without continuous or repeated connection to the ground. By my understanding, all gliders before that time had enough drag that even naturally-occurring thermals would have been insufficient to keep them aloft.