Idaho is a strong favourite to give prolific trainer Aidan O'Brien a fifth St Leger victory at Doncaster on Saturday.
O'Brien trains a third of the field of nine horses for the final British Classic of the flat season and Idaho heads the market for the prestigious race, run over a mile and six furlongs.
Idaho finished third in the Epsom Derby before crossing the line in second place in the Irish Derby and going on to win the Great Voltigeur at York last month.
The three-year-old colt will be ridden by Seamie Heffernan after O'Brien revealed that Ryan Moore would be in action at Leopardstown.
Leading Light was the fourth St Leger winner for O'Brien three years ago and the Irishman is optimistic that the odds-on favourite will handle the step up in trip in a Group One which offers £396,970 prize money for the winner.
"It's gone well with Idaho and everything has been smooth since York. He is a clean horse and he has come out the race great," said O'Brien.
"We were happy with him going there. We were hoping he would have a nice race and come forward and we've been happy with him since.
"You can never be confident [getting the trip] but we always thought he would."
O'Brien also saddles Housesofparliament, second behind stablemate Idaho in the Voltigeur following a win at Newmarket, and Queen's Vase winner Sword Fighter.
The John Gosden-trained Muntahaa would appear to be the best of the rest, having scored at Chester last time out and the forecast of rain will be a positive for him.
Gosden also has four St Leger successes to his name and Paul Hanagan has the job of attempting to steer Muntahaa to a fifth this weekend.
Laura Mongan will bid to become the first female trainer to win the world's oldest Classic with Harbour Law, while Ventura Storm goes in search of a third consecutive win for Richard Hannon under champion jockey Silvestre de Sousa.