Envisioned as a luxury sports car, the Triumph Stag was designed to compete directly with the Mercedes-Benz SL class models. All Stags were four-seater convertible coupés, but for structural rigidity – and to meet new American rollover standards of the time – the Stag required a B-pillar "roll bar" hoop connected to the windscreen frame by a T-bar. A removable hardtop was a popular factory option for the early Stags, and was later supplied as a standard fitment.
The car started as a styling experiment cut and shaped from a 1963–4 Triumph 2000 pre-production saloon, which had also been styled by Michelotti, and loaned to him by Harry Webster, Director of Engineering at Triumph. Their agreement was that if Webster liked the design, Triumph could use the prototype as the basis of a new Triumph model. Harry Webster, who was a long time friend of Giovanni Michelotti, whom he called "Micho", absolutely loved the design and spirited the prototype back to England.