Final answer:
Zoser's mortuary complex is unique for being designed by architect Imhotep and is the earliest large-scale cut stone construction, marking a significant evolution in Egyptian tomb design.
Step-by-step explanation:
A unique feature of Zoser's mortuary complex, commonly known as the Step Pyramid complex, is that it was designed by the architect Imhotep and is considered the earliest large-scale cut stone construction. It marks a significant departure from previous traditional flat-roofed mastaba tombs, progressing towards more ambitious pyramid structures. Not only did it set the precedent for future Egyptian pyramid designs, but it also stands as the oldest Stone Age edifice in Egypt.