` ` Monsters vs. Aliens '' is about motley crew of monsters who team up to fight alien . Those assets become apparent when an alien invader ( voiced by Rainn Wilson of `` The Office '' ) decides he wants Earth , and the monsters -- Ginormica , Dr. Cockroach ( `` House '' star Hugh Laurie ) , The Missing Link ( Will Arnett ) , and the gelatinous B.O.B . Monsters are led by almost 50-foot woman , voiced by Reese Witherspoon . Witherspoon says she hopes character can be role model for girls . Other actors and voices : Seth Rogen , Kiefer Sutherland , Will Arnett .
` ` Monsters vs. Aliens '' is about motley crew of monsters who team up to fight alien . Monsters are led by almost 50-foot woman , voiced by Reese Witherspoon . Witherspoon says she hopes character can be role model for girls . Other actors and voices : Seth Rogen , Kiefer Sutherland , Will Arnett .