FACTBOX - Main candidates in Serbia's presidential election

(Reuters) - Serbs vote on Sunday in a presidential election, with opinion polls giving hardline challenger Tomislav Nikolic a slim lead over pro-Western incumbent Boris Tadic, but not enough for a first-round victory.

Here are profiles of the main candidates:

TOMISLAV NIKOLIC (Radical Party)

Orientation: nationalist, eurosceptic

Promises: keep Kosovo within Serbia but without going to war; fight crime, corruption; promote employment and people-friendly economic growth strategies.

Quote: "If I win these elections, it is Serbia that will win, not Moscow, not Brussels, not Washington."

Slogan: "With all our heart"

Recent poll figures: around 33 percent

BORIS TADIC (Democratic Party)