The main villain in Power Rangers: Time Force is Ransik.
Ransik is a mutant criminal from the year 3000, where humans and mutants live in a deeply unequal society. After being captured and sentenced to cryogenic imprisonment, he escapes with several followers, steals a time ship, and travels back to 2001. His arrival creates the central conflict of the series.
The Time Force Rangers—Jen Scotts, Lucas Kendall, Trip, and Katie Walker—pursue Ransik into the past. Because their morphers require the DNA of their fallen teammate Alex, they recruit Wes Collins, whose genetic link allows the team to transform. Ransik's gang includes Nadira, Frax, and Gluto, although Ransik is the leader and principal antagonist.
A common mix-up is confusing Ransik with the villains of other Power Rangers eras. Astronema belongs primarily to Power Rangers in Space, Mesogog is the major villain of Dino Thunder, and Lothor leads the antagonists in Ninja Storm. Ransik is portrayed by Vernon Wells and eventually receives a more complicated redemption arc than a typical franchise villain.