The Doctors are in the essential and unofficial guide to Doctor Who's greatest Time Lord
"From his beginnings as a crotchety, anti-heroic scientist in 1963 to his current place in British pop culture as the mad and dangerous monster-fighting saviour of the universe, the titular character of Doctor Who has metamorphosed in his 50 years on television. And yet the questions about him remain the same: Who is he? Why does he act the way he does? What motivates him to fight evil across space and time?"--Amazon.com.