Thaleia is a mermaid from a movie A Mermaid's Tale, played by a Nancy Stafford. Younger Thaleia in flashbacks is played by Lauren Zbylski.
Thaleia met a firsherman Art in her teens, and they fell in love. Thaleia spent a lot of time on land, but was found out by her father and forbidden to do so in future. Thaleia however had gotten pregnant by Art, and bore him a son, since the child was human, she secretly left the boy at Art's door.
Coral found a friend named Ryan on land and brought her to the hidden mermaid island. At first Thaleia forbid the girl to return to mainland, but after hearing that she is the granddaughter of Art, she allowed Ryan to return, if she kept them a secret. Ryan returned quite soon however, as Art had an heart-attack on sea while rescuing Coral from the net. Art's son Matt also came to the island, and it was then Thaleia revealed herself to them, and allowed the mermaids to heal Art with their magic. Thaleia then revealed herself to be Matt's mother to Matt. From that day on Thaleia changed the mermaid laws on interacting with humans.