Slaar was the main antagonist of the Doctor Who story "The Seeds of Death".
He was portrayed by the late Alan Bennion, who also portrayed the series' other Ice Lord antagonist, Commander Azaxyr.
Slaar was the leader of the group of Ice Warriors who took over the T-Mat control station on the moon, which provided instant transportation to all major Earth cities, some time in the mid-21st century. He reported to a Grand Marshall, who commanded the main invasion force of which Slaar led the spearhead. After killing some of the technicians who resisted, Slaar ordered the base controller, Osgood, to establish a T-Mat connection with Earth. Osgood instead destroyed the controls so Slaar had him killed. The assistant controller, Fewsham, was willing to assist Slaar in order to save his own life but the other surviving technicians, Phipps and Locke, attempted to send a warning message to Earth. Slaar stopped them and had Locke killed, although Phipps managed to escape.
Once Fewsham managed to get an emergency channel open, Slaar and his men hid while T-Mat's chief technician Gia Kelly arrived to effect repairs. They then took Gia prisoner and killed her assistants. Slaar had Fewsham despatch a number of seed pods to various locations on Earth, where they released poisonous spores that killed everyone in the immediate vicinity and began to grow a fungus that was slowly destroying Earth's atmosphere, making it hostile to humans but habitable by Ice Warriors. The Doctor was captured after making it to the moon by rocket and ordered to work with Fewsham. When he attempted to sneak a look at the seed pods, Slaar allowed him to view one which then released its spores, knocking him out. Slaar attempted to kill him by ordering Fewsham to T-Mat him into space but he was rescued by Jamie and Phipps. He also sent an Ice Warrior to London to destroy the weather control station, since the seed fungus could be destroyed by rainfall.
Slaar and his men were temporarily weakened when Zoe increased the temperature, allowing the Doctor and the other surviving humans to escape back to Earth, although Fewsham remained behind. Slaar was preparing a signal beacon that would bring in the Grand Marshall's fleet. Fewsham deliberately allowed those on Earth to eavesdrop on its test and learn the signal. When Slaar realised what he had done, he had Fewsham killed. The Grand Marshall chided him for this, since they still needed a human to operate T-Mat.
As a result, when the Doctor returned to the moon, Slaar kept him alive. However, the Doctor prevented Slaar's beacon from broadcasting, meaning the Ice Warrior fleet followed a fake beacon sent up by the humans which lured them into the sun, killing all of them. Furious, Slaar ordered his last remaining Ice Warrior to kill the Doctor. At that point, Jamie arrived and he and the Doctor grappled with the Ice Warrior. During the struggle, the Ice Warrior's gun went off and the blast hit Slaar, killing him.