WrestleMania is considered World Wrestling Federation's (WWF, now WWE) flagship event, having first been held in 1985. It has become the longest-running professional wrestling event in history and is held annually between mid-March to mid-April. It was the first of WWF's original four pay-per-views, which includes Survivor Series, Royal Rumble, and SummerSlam (the first also being introduced in 1987, with the other two being introduced in 1988), which were eventually dubbed the "Big Four". It eventually became described as the Super Bowl of sports entertainment.