Traditionally at weddings, the groom chooses friends to act as ushers, but Prince William won't have this option, making it one less decision he'll have to make for the royal wedding.
Gentlemen ushers are used for state banquets and ceremonies, including royal weddings, according to People magazine. Each member of this 10-man group is chosen from the three branches of the Armed Forces, and appears in full uniform for the ceremony. Gentlemen ushers have worked for the royal family since the 15th century, when they were assigned to stand at the doors of whatever room the monarch occupied.
For the royal wedding of Prince William and Kate Middleton, the "gentlemens'" main assignment will be to guide guests to their seats. According to tradition, members of the royal family are seated on the right side of Westminster Abbey.
In other words, none of the prince's friends who chose William to usher at their weddings will get to repay the favor.