Thals were one of the two humanoid races which originally inhabited the planet Skaro (the other being the Kaleds).
Physical characteristics
History
The Thals lived on the same planet as the Kaleds and eventually came into conflict with them. The early parts of the war were fought with highly advanced weaponry, such as nuclear weapons, though after a thousand years they were running low on supplies and had to resort to more primitive weapons.
Near the end of the war, Davros gave the means to destroy the Kaled city to the Thals. They used this compound in the missile they sent to the Kaled city, which destroyed it. In "retaliation" for the destruction of the base, Davros ordered the Daleks to destroy the Thals. The survivors were able to blow up the bunker where Davros was, trapping him and the Daleks in for thousands of years.
Culture
The Thals were nearly as brutal as the Kaleds. They had no qualms about using the slave labour of Kaled prisoners and Mutos to build a radioactive bomb.