Example is Ursula Le Guin's Wizard of Earthsea, traditional demonology etc. This is the main tenet of classic hermetic magick, and much of shamanism. If a mage knows the true name of something, it will be in his control. Finding true names is of course quite hard, and different traditions have different methods. Dreamspeakes make journeys into the Umbra to seek out the spirits and ask them to reveal the name.
Hermetic mages delve into ancient tomes, trying to find the true name recorded somewhere.
There are certain words that are able to change and influence the inner and outer reality of those saying them. The power is said to lie in the sounds that compose the words. Another hermetic thought, and also used by the Nephandi. The mage chants ancient or incomprehensible formulas, which by their incomprehensibility and alienness gain power. Such invocations can be found in many libraries or passed down the tradition.