Who is often considered one of the pivotal figures in Mississippi's architectural history?

W.M. McCardle is recognized as a pivotal figure in Mississippi's architectural history due to his significant contributions to the state's architectural landscape during the late 19th and early 20th centuries. His designs often reflected a mix of styles, incorporating elements that spoke to both regional influences and broader architectural movements of the time.

McCardle was instrumental in shaping the architectural identity of Mississippi, particularly through his work in Jackson and other areas, where his buildings often featured innovative designs that responded to the local environment and cultural context. His legacy includes not only individual buildings but also an impact on the direction of architecture in Mississippi as a whole. This positions him as an essential figure in understanding the evolution of the state's architectural heritage.

In contrast, figures like Frank Lloyd Wright and Louis Sullivan, while immensely talented and influential in the broader American context, were not specifically tied to Mississippi’s architectural developments. Similarly, Richard Meier is known for his modernist designs, but his work does not directly connect to the unique historical architecture that defines Mississippi. Therefore, McCardle’s focused imprint on Mississippi architecture makes him the correct answer.