Thace is a member of the Galra Empire under the command of Prorok. However, he worked in secret to help the Paladins to escape by sabotaging the Galra's attempts to capture Voltron.
He is later revealed to be a rebel and spy, implanted into the Galra Empire ranks while spying for the Blade of Marmora, a secret group of Galra rebels who are against Zarkon and his tyranny.
He later sacrifices himself to save Keith and cause the power core of Zarkon's ship to overload and explode.
Thace scrambling the fighters
Thace realizing a Lion has breached the hull
Real heroes die with a smile.