Who is the greatest racehorse of all time?

it depends on the socio economic times of different countries, in the depression people were looking for a hero to worship, sea biscuit in the usa, phar lap in australia and new zealand, and then later on secretariat, bernborough,kindergarten, and probably europe and england had their champions,and in later times seattle slew,sunline , manikato and a host of others. good question, but tough to answer