Thaleia, aso known as Thelia was one of the nine Mousai, along with : Kalliope, Kleio, Ourania, Melpomene, Polyhymnia, Erato Euterpe, and Terpsikhore. These are the goddesses of music, song and dance. Thelia’s name had derived from the Greek word thaleia; meaning « rich festivity » or « blooming ». When the Mousai were assigned specific tasks Thalia became the Muse of comedy and bucolic poetry. In this guise she was portrayed with the attributes of comic mask, shepherd's staff and wreath of ivy.
At the first meeting between Harley Quinn and Thelia, Thelia was amused by the feistiness of the adorable character. She is of course the goddess of comedy and Harley does in fact represent a Harlequin, so they were a match made in heaven. Thelia grants Harley some of her powers in return for saving the Gods. Harley had help of course from Mary Marvel and Holly Robinson.