Which car was the Ford Mustang's direct rival introduced by Chevrolet in 1967?

Chevrolet’s direct rival to the Ford Mustang, introduced for 1967, was the Chevrolet Camaro.

The Camaro was Chevrolet’s entry into the fast-growing pony-car market created by the Mustang. Chevrolet announced the car in June 1966, and it went on sale on September 29, 1966, as a 1967 model. Its conventional front-engine, rear-wheel-drive layout matched the formula that had made the Mustang so successful.

The first-generation Camaro used General Motors’ new F-body platform and was offered as a two-door hardtop coupe or convertible. Buyers could choose a standard inline-six or several V8 engines. Performance versions included the SS package and the Z/28, which used a high-output 302-cubic-inch V8 developed with Trans-Am racing in mind.

The Pontiac Firebird is a common alternative in this question, but it was not Chevrolet’s separate rival: it was Pontiac’s closely related F-body sibling, also introduced for the 1967 model year. The Corvette and Chevelle occupied different positions in Chevrolet’s lineup.