Alexi Constantinou, also known as Little Alexi, was the captain of the Callisto. As a boy, he was friends with Kostas Krimboti and Yanni Karopolis. Alexi came from a wealthy family, and joined the Greek Navy.
In his adult life, Kostas and Yanni humiliated him in front of his navy crew by blasting their cannons at his ship and knocking him in the water; they also dubbed him "Little Alexi".
Alexi vowed his revenge, however when he came across the Blue Turtle, Ben and Ned managed to fool him into thinking there was a sickness on board.