The Mustang is one of Ford's crown jewels and perhaps one of the most significant cars of all time.

But now the Mustang name is about to enter an entirely new era, and not everyone is happy about it.

Ford's recent decision to add a four-door electric sport utility vehicle to its Mustang lineup has some sports car purists up in arms, echoing the outrage over SUVs introduced in the past by other performance car brands such as BMW and Porsche.

But Mustang sales have fallen off a cliff since the car's most recent redesign in 2015. This is no fault of the car itself, said AutoPacific analyst Ed Kim. The Mustang's segment is simply shrinking. Sales of two-door sports coupes is falling along with other traditional passenger car segments, and sales of SUVs are rising.

BMW's sport utility vehicles, for example, made up 37.3% of the brand's sales in 2018, an increase over the 33.8% in 2017. In 2018, Porsche sold 34,237 Macan and Cayenne SUVs combined in the U.S., compared with just 22,965 of all three of its passenger car lines — the Panamera sedan, the 718 sports car and the legendary 911.

Meanwhile Ford also sees in the Mustang a way to make an electric that will inspire enthusiasm among buyers, rather than simply enable the company to meet emissions requirements. Automakers are frenetically making electric vehicles to both comply with increasingly stringent rules around the world and stave off competition from hyped-up electric carmakers such as Tesla.

"It started out as a compliance product," said Dave Pericak, who is the global director of the automaker's Icon vehicles program. "But very quickly, this thing started to become something that we realized [wasn't] going to be an amazing machine or something that was going to be desirable. So we scratched those plans and went back to the drawing boards and asked: How do we do something that will inspire and be exciting? And so we talked about Mustang."