A scientific expedition in Antarctica transmitted photos of the Krynoid pod they had discovered to Thackeray, and Thackeray insisted that the Fourth Doctor should go and investigate. After learning the threat the Krynoid posed to the world, he called in UNIT to deal with it, and went to Harrison Chase's mansion to view the attack.
The Doctor later invited Thackeray to travel with him and Sarah Jane Smith in the TARDIS for a holiday, but he declined because his wife was expecting him home for tea. Perhaps this is just as well, bearing in mind the TARDIS arrived in Antarctica instead of the intended holiday destination of Cassiopeia. (TV: The Seeds of Doom)
After the events of the Krynoid's attack, he ordered cuttings to be taken from Krynoid remains, which were later stolen and eventually used for research by environmentalist Alex Marlowe.