Karl Berngardovich Radek (October 31, 1885 – May 19, 1939) was a Marxist active in the Polish and German social democratic movements before World War I, and an international Communist leader in the Soviet Union after the Russian Revolution.
Really useful book for understanding the clashes between the Bolsheviks and Kautsky along with the pressures faced in the early years of the Russian Revolution. The footnotes are very helpful.