Alfred North Whitehead (1861–1947).

The birth of logicism -------------------------
Russell would not have been Russell without his teacher and later colleague, Alfred Whitehead. This British philosopher, logician and mathematician entered Trinity College, Cambridge, in 1880, where he excelled in every subject, particularly literature, philosophy, theology and mathematics. While still a student, he took an interest in Maxwell's research, but soon became fascinated by the early development of modern algebra, culminating in his Treatise of Universal Algebra, published in 1898. His outstanding results in the Mathematical Tripos (a highly selective examination; see Tangente 137, 2010) earned him a place on the teaching staff as early as 1884.
In 1890, the young Russell also entered Trinity College. Student and teacher discovered a shared passion for the foundations of mathematics and logic. This marked the beginning of a fruitful collaboration that would last some twenty years—the most productive period of Whitehead's mathematical career. Their joint research produced Principia Mathematica, the work that established logicism.