The Ruf CTR also known as the CTR Yellowbird or simply Yellowbird, is a limited-production, high performance sports car manufactured by German automobile manufacturer Ruf Automobile. Introduced for the 1987 model year and based on the Porsche 911, the CTR featured an enlarged and highly tuned version of Porsche's 3.2 litre flat-six cylinder engine, lightened body panels, an integrated roll cage, upgraded suspension and braking systems, a custom-designed transmission, and several unique trim pieces such as polyurethane bumpers, and the use of the side-mounted oil filler necessitated by relocating the oil tank forward to clear the intercooler on that side.

Ruf Automobile GmbH is a German car manufacturer. Formerly using Porsche bodies in white to build cars, today they build vehicles on their own bodies and chassis. They also manufacture performance parts for various Porsche models, including the 911, Boxster, and Cayman.