The Fatal Five
From superman.nu: Supermanica
A group of 30th-Century super-villains who have battled the Legion of Super-Heroes on numerous occasions.
The Fatal Five are Mano, Emerald Empress, Tharok, Persuader, and Validus.
Superboy and the Legion first encounter the Fatal Five in January-February, 1967 (Adv No.352-353: "The Fatal Five, Parts I-III: To Save a Galaxy; An S.O.S. to Evil; and Slain by the Sun-Eater").