The Javelin replaced the Marlin. Both were designed to compete with the Ford Mustang and the Barracuda. They were both American Motors cars. I don’t believe Iacoca was involved with the design of either.
I searched it and the designer was Dick Teague. He also designed the Pacer, Gremlin and one I was trying to remember: the Hornet. Wasn’t it an extended/longer Gremlin?
Richard A. Teague designed the Javelin.