Which Scottish architect developed the neoclassical 'Adam style'?

The Scottish architect who developed the neoclassical Adam style was Robert Adam.

Robert Adam studied ancient architecture during a lengthy stay in Rome from 1754, working with artists and architects including Charles-Louis Clérisseau and Giovanni Battista Piranesi. After returning to Britain in 1758, he established a London practice with his brother James and shaped a lighter, more decorative form of neoclassicism.

The Adam style unified architecture, interior decoration, furniture, fireplaces, carpets, and fittings into a coordinated whole. Robert also promoted the idea of “movement,” using changing room sizes, ornament, and spatial contrasts to create visual variety. The brothers published examples of their work in Works in Architecture, beginning in 1773.

The family names can cause confusion. William Adam, Robert’s father, was an important earlier Scottish architect, while James Adam was Robert’s principal collaborator. John Adam, another brother, also worked in the family practice, but Robert is the figure most commonly credited with developing the style.