It's time for mollecular transmutation! Triceratops!―One of Billy's roll calls.[src]

William Billy Cranston is the first Blue Ranger of the Mighty Morphin Power Rangers in the 'modern era', during Switching Places, Billy accidentally switch bodies with Kimberly Ann Hart becoming (temporary) the Pink Ranger, he later became the first Blue Ninja Ranger of the Ninja Rangers.

The Blue Ranger is a title given to a character in every Power Rangers series who usually serves as the second-in-command of the team, even though other colors have been known to share the role. While the original Blue Ranger was a serious team member and represented The smart one, some other subsequent Blue Rangers have been pushed to other positions, such as a comic relief character or a laid-back type of character. Blue Rangers are generally male, however, some seasons have had female Blue Rangers. So far, female Blue Rangers wear a lighter shade of blue than their male counterparts, although Cestro, as the Blue Aquitar Ranger, also wore a lighter shade of blue similar to that of the female Blue Rangers. Weapons used by Blue Rangers are mainly dual or wide ranged weapons, though some have used blasters and shields as their weapons. Blue Rangers also receive special gear like those of Red and Green Rangers.