Donald Sertori a fisherman, with several boats. One boat was captained by Eddie, who fished at the wrong places and with wrong nets, when Cleo caught him, she told her dad and Eddie was fired. He hates teenage boys and will keep his daughters away from them until they're old enough, though except for Lewis.
In the second season, he and Bev Sertori are divorced, and the girls are living with him. At one point he met with Annette Watsford and wanted to sell fish to her restaurant. The girls thought that they were dating, and Cleo ruined the dinner, which made Annette withdraw from the deal. Later Cleo, Emma and Rikki showed Annette table a full of seafood, made from Don's fish, and got the deal back.
In the third season, he gets married to Samantha Sertori. He also becomes a pirate at the marine park as a second job, to gather money for family vacation. He was constantly tired after taking that job. After seeing that his success had an effect on Cleo's dolphin show, Don quit as a pirate and suggested that Cleo wore a pirate costume instead on her show. He is a big fan of Elvis Presley and Classic Rock.
Don has a kindly, jolly personality. He is protective of his daughters and make sure boys treat them right. Although he was initially hostile towards Lewis, he later warms up to him through their mutual interest in fishing. He even encourages Lewis to go after Cleo when he blanks out on asking her to the dance and she goes with Nate instead. He is shown to be very supportive of their relationship and even states that he is like part of the family and that he could not have asked for a better boyfriend for Cleo then him. He is generally very supportive, but unaware of Kim's wrongdoings and blames.
- Don hates teenage boys who will try to woo his daughters, the reason behind this is unknown, most likely to protect his daughters until they're old enough, he didn't even like Lewis hanging out with Cleo at first, though he did reconsider him later on after he proved much of himself to be worthy enough to be with Cleo.
- Don's full name Donald was revealed in an episode "To Have And To Hold Back".
- Main article: Donald Sertori/Gallery