Sheikh Mohammed bin Rashid Al Maktoum has spent millions trying to win the Kentucky Derby, and in the process plowing money into horse racing worldwide. Now with the overwhelming favorite, Dubai’s ruler faces increased scrutiny for allegations that he has violated human rights and orchestrated the disappearance of his own daughter. The controversy, well-known in the Middle East for a more than a year, has gotten renewed attention as Essential Quality prepares for Saturday’s race. The Kentucky Horse Racing Commission received a complaint on Wednesday from a group of human rights attorneys and students at the University of Louisville seeking...