King Kong is well known for its groundbreaking use of special effects, such as the use of stop-motion animation, matte painting, rear projection and miniatures which were all conceived before the digital age.

All creatures of Skull Island were brought to life through the use of stop-motion animation by Willis O’Brien and his assistant animator, Buzz Dixon. The stop-motion animation scenes were painstaking and difficult to achieve and complete, because the special effects crew realized that they couldn’t stop, because it would make the movements of the creatures seem inconsistent and the lighting wouldn’t have the same intensity over the days. A device called the surface gauge was used in order to keep track of the stop-motion animation performance. The iconic fight between Kong and the T-Rex took seven weeks to be completed.

More Info: en.wikipedia.org