In the once-upon-a-time days of the First Age of Magic, the prudent sorcerer regarded his own true name as his most valued possession but also the greatest threat to his continued good health, for -- the stories go -- once an enemy, even a weak unskilled enemy, learned a sorcerer's true name, then routine and widely known spells could destroy or enslave even the most powerful. -- VernorVinge, in the short story "True Names"
Vinge was talking about "The Wizard of EarthSea", but NameMagic is a very old idea; Le Guin did not invent it, either.
For several years (ever since reading "Ursula K. Le Guin's A wizard of Earthsea") I've had the idea that the "true names" of fantasy were like objects in a database. -- VernorVinge, written 1999 in an Introduction to a republication of "True Names"
See also: NameMagic, ControlFreak, PasswordCapabilityModel.