Friday Trivia Challenge for 10/30/15

This excellent but luckless racer won six Grade I races in a single season and was the top money earner of that year in North America, yet was left out during year-end championship voting despite having beaten both the Horse of the Year and the champion of one of the divisions for which he was eligible during the course of his campaign. In the other division for which he was eligible, he posted four Grade I wins to the champion's two. Name him.