Which of the management theorists attending the dinner developed the idea that there are five functions of management: planning, organizing, commanding, coordinating, and controlling?

The management theorist responsible for conceiving the five functions of management is Henri Fayol.

Henri Fayol is a French engineer who created an entire branch of business administration theory commonly referred to as Fayolism. This also includes his five functions of management theory, which was published in his book General and Industrial Management, first published in France in 1916.