While attacking Sailor Moon and Tuxedo Mask, Neflite sent Leo the Lion after them. Sailor Moon used Moon Tiara Magic on him. It knocked him backwards, but did not kill him. They escaped into the elevator, and Neflite recalled Leo the Lion.
His name is derived from the constellation, Leo the Lion.
Leo the Lion is the first male Negamonster (or monster of the week, at that). He is also the first Negamonster not sent to gather energy, and the first monster of the week to survive an episode (only one other survives an episode, and dies in the following episode).