The Ronans were a race of large, highly intelligent, ape-like creatures from the planet Ronos. Ronos was a dry planet without seas and a spiral orbit that took it ever further away from its sun. As the planet grew colder the Ronans drilled through the planet's crust to release the energy from the core. This attempt to save the planet led to its destruction. Ronos and Ronans died out.
A small craft of Ronans escaped before their planet's destruction. Encountering the Earth, they sought to repeat the action by drilling down into the planets core beneath the Dead Sea using the local people as slaves. The Fourth Doctor's intervention saw their network of tunnels flooded with salt water and the Ronans driven underground, trapped by the salt water they were allergic to. (PROSE: The Heat-Seekers)