Lek Viriyaphan (Thai: เล็ก วิริยะพันธุ์, sometimes referred to as Khun Lek; 1914 – 17 November 2000) was an eccentric Thai businessman, millionaire and patron of culture responsible for the construction of Ancient Siam, Erawan Museum and Sanctuary of Truth.

He accumulated professional knowledge and understanding of arts, religions, philosophies and cultures since an early period of his life.

Later, through work relationships he met his wife and lifelong friend Prapai Viriyaphan, who became a partner and inspiration throughout his business career.

This inspired him to build the Ancient Siam open-air museum park in Samut Prakhan, Thailand.

He has left his descendants a thriving group of companies that is still developing: besides expansion of a plant in 2017, the construction of the first factory producing batteries for plug-in hybrid electric vehicles in Southeast Asia was announced where Mercedes-Benz had invested 100 million Euros.