Zordon

Fought in a war against Rita Repulsa, banished into a time warp by her;
Could only communicate with the outside world through an energy tube
Chose teenagers to become Power Rangers when Rita returned to conquer Earth
Returned to Eltar, a year after the defeat of the Machine Empire
Captured by Dark Specter, when Eltar was conquered
Had Andros break his energy tube, causing a Z-wave that purified most of the universe