Until 2008 when he formed his own party, Nikolic - a one-time ally of late Serb strongman Slobodan Milosevic - was the number two in the ultranationalist hardline Radicals whose leader Vojislav Seselj is on trial before the UN war crimes tribunal in The Hague.
Since breaking with the Radicals, Nikolic transformed himself from an anti-Western hardliner to a conservative pro-European Union nationalist.
"In this region, the ghosts of the past always reign ... The past will follow Nikolic like a shadow," said Bosnian Serb political analyst Tanja Topic.
The fragile process of reconciliation between the former foes from the 1990s Balkan wars - Serbia, Croatia and Bosnia - started during the eight-year rule of Nikolic's predecessor, Boris Tadic, could slow down, analysts warn.
Although he avoided using the term genocide in public, Tadic apologised to Srebrenica victims when he attended the 2005 commemoration of the massacre, the bloodiest episode in the 1992-95 Bosnian war.
"Nikolic has to prove himself... (as a) politician ready to build a better co-operation with Serbia's neighbours," said Croatian daily Jutarnji List in an opinion piece.
It warned the Serbian leader must not count on the Balkan countries forgetting what has happened: "Reconciliation should be built on a condemnation of past crimes, not oblivion".
Last week Croatia was shaken by Nikolic's remarks to a German paper that Vukovar - a town that for many Croats is a symbol of the horrors of the 1991-1995 war with rebel Serbs - was a "Serb town" and Croat refugees "did not have to return there".
Croatian President Ivo Josipovic said he hoped the Serb leader "will revise his attitudes".
- AAP
