Santos Primo Amadeo Semidey (June 9, 1902 – August 25, 1980), a.k.a. "Champion of Hábeas Corpus," was an attorney and law professor at the University of Puerto Rico, a Senator in the Puerto Rico legislature, and counsel to the American Civil Liberties Union branch in Puerto Rico, established in 1937. He founded the Phi Sigma Alpha fraternity in Puerto Rico.