Best Villains of all time they are
Shiro / The Clone--- Shiro used keith since day one when they 1st meant. when he was fighting Keith as a clone he told Keith that I should’ve abandoned you, just like your parents did. They saw that you were broken, worthless. I should’ve seen it, too. Shiro must known more of Keith's Father. Plus he tried to kill Keith. He's a Spy and a clone from the Galra Empire from Haggar, could he always been a spy from the Galaxy Garrison?
Haggar -- She Torture peoples, she used Lotor dead body inside a mech, she almost destroyed all realities
Lotor---- He experiment on the colony Alteans , he jump around in the quintessence field many times that tear the galaxy.
Zarkon-- Torture, killer, taken over the galaxy,
Wade -- Sky Marshal of Galaxy Garrison in Voltron Force responsible for decommissioning Voltron after the final defeat of King Lotor because he sabotaged the Lions turning the public turn against Voltron, He made his own Lion , the attempted destruction of Earth, kidnappings, illegal and unlawful imprisonments
Maahox -- Revived Lotor many times