The author tells the 2000-year old history of one  of  mathematics’ most  elusive numbers, the square root of minus one, also  known  as  i, re-creating  the baffling mathematical problems that conjured  it  up  and the colourful characters who tried to solve them. Addressing readers with both a general and scholarly interest in mathematics, Nahin weaves into this  narrative entertaining  historical facts, mathematical discussions, and the application of complex numbers and functions to important problems.