Skaag is an Ice Grand Marshal


Grand Marshal Skaag joined forces with Ice Lord Slaar, to lead the invasion on T-Mat, a transmat station, to spread lethal seed pods all over Earth. These would wipe up humanity, leaving the Ice Warriors to colonise the planet

Skaag was killed when the 2nd Doctor hijacked Slaar's homing beacon, sending Skaag and the Ice Warrior fleet flying into the Sun