The last Triple Crown winner was Affirmed in 1978.
Big Brown is the first 3-year-old since Smarty Jones in 2004 to go into the Belmont Stakes with a chance to sweep the three races.
One possible contender in the Belmont Stakes is Peter Pan Stakes winner Casino Drive.
"He just ran a big race," Big Brown trainer Rick Dutrow Jr. said of Casino Drive. "He's going to have to come back in a month off that race, which isn't going to be easy for him, When horses have to sit a long time, their next race might not be so strong. I'd like to have the horse, but I don't see him beating Big Brown."
Casino Drive is a half-brother to Jazil and Rags to Riches, the winners of the last two Belmont Stakes.