The Motorola RAZR was announced as the thinnest smartphone upon its release, but is soon to be replaced by a phone made and designed in China - the Oppo Finder. It measures in at a 6.65mm, 0.45 mm less than the Motorola Razr.
But - that's only one part. It also is pretty strong, acting as a hammer as well, dethroning Nokia from their position. Even though it's this thin and strong, it also is pretty powerful, using a dual-core 1.5 GHz CPU with 1GB of RAM, 16GB of internal storage, and Android 4.0.
Here's a demo video: