Dr. Xeno Houston Wingfield (Dr.ドクター ゼノ・ヒウストン・ウィングフィールド Dokutā Zeno Hiusuton Wingufīrudo) is a scientist and the former leader of the American Colony, and currently one of the leading scientists for the Kingdom of Science.]Xeno is the main antagonist of the New America City Arc and an uneasy ally of Senku's in the South America Arc, later becoming a proper ally in the New Stone World Arc.

Stanley Snyder (スタンリー・スナイダー Sutanrī Sunaidā) is an ex-military officer working for Dr. Xeno.[11]

He is the one who initially assaults Senku's group once they disembark on the territory of the former United States.[12] Once Xeno has been captured by the Kingdom of Science, Stanley pursues them on their way to South America in order to retrieve his longtime friend and leader.

Charlotte Bony (シャーロット・ボニー Shārotto Bonī) is one of the former members of the American Colony and was part of an elite unit prior to the Petrification.[5] She's overzealous and appears to idolize Stanley Snyder. She is currently a member of the Kingdom of Science.

Ibara (イバラ) is the former minister of the Petrification Kingdom and the main antagonist of the Treasure Island Arc.

Initially serving as minister to the Head of the Kingdom, he usurped power by using the petrification device on the latter and establishing a dictatorship over the island.