Rudolf Joseph Lorenz Steiner (25/27 February 1861 – 30 March 1925) was an Austrian philosopher, social reformer, architect, and esotericist. Steiner gained initial recognition as a literary critic and cultural philosopher. At the beginning of the 20th century, he founded a spiritual movement, anthroposophy, as an esoteric philosophy growing out of idealist philosophy and with links to theosophy.

Steiner led this movement through several phases. In the first, more philosophically oriented phase, Steiner attempted to find a synthesis between science and mysticism; his philosophical work of these years, which he termed spiritual science, sought to provide a connection between the cognitive path of Western philosophy and the inner and spiritual needs of the human being. In a second phase, beginning around 1907, he began working collaboratively in a variety of artistic media, including drama, the movement arts (developing a new artistic form, eurythmy) and architecture, culminating in the building of the Goetheanum, a cultural centre to house all the arts. In the third phase of his work, beginning after World War I, Steiner worked to establish various practical endeavors, including Waldorf education, biodynamic agriculture, and anthroposophical medicine.