EFEBy Jaime Ortega Carrascal Bogota

Six candidates will square off in Sunday's presidential election in Colombia, a contest in which a popular appetite for change has given former guerrilla Gustavo Petro the lead in the polls and a golden opportunity to become the Andean nation's first leftist head of state.

In a country beset by a decades-old armed conflict and drug trade and where corruption, poverty and inequality triggered a wave of social protests last year, Petro has found fertile ground for his message of societal transformation.