Lisa Morel (first appearance: Adventure Comics (vol. 1) #266 (November 1959)) was among several violet-eyed Atlantean children who were born unable to adapt to the watery world, and would soon die. To save them, they were ejected in waterproof lifeboats to the surface, to live among land-dwellers. Lisa was adopted by the scientist Hugo Morel and his wife.
When Aquaman was in danger, her water-breathing and telepathic powers awakened. She made herself a costume identical to his, took on the name "Aquagirl" and fought alongside him. But her newfound powers were short-lived, and she permanently lost them. She is not considered to have been active as Aquagirl in current continuity.
Selena (first appearance: World's Finest Comics #133) was a young Poseidonis teenager who teamed up with Aquaman under the name "Aqua-Girl" in order to impress her boyfriend and become a superheroine. However, as with Lisa Morel, Selena only appeared once and was never mentioned again. She is also not considered to have been active as Aqua-Girl in current continuity.
Tula is the first canonical Aquagirl. After losing her parents soon after her birth, she is found and adopted by one of the royal families of Atlantis. Given the title of princess of Poseidonis, Tula is schooled in Atlantean traditions. She never leaves the royal palace until she meets Aqualad at age 15.
Tula sometimes helps Aqualad with missions during his time with the Teen Titans; eventually, she also becomes an honorary member. She takes the name Aquagirl to honor her boyfriend as well as Aquaman. When Aquaman leaves his throne to search for his then-missing wife Mera, Nakran takes over Atlantis as a dictator. His reign falls only when Tula leads a rebellion against him. Tula continues her life after this, resuming her life with Garth (Aqualad) when he returns to Atlantis. She continues to be an ally to Garth and the Teen Titans. She and Garth aid the Titans in bringing down the H.I.V.E. once and for all.
During the Crisis on Infinite Earths mini-series, Aquagirl is killed by the villain Chemo after she drowns in water that he has poisoned.
Years later, in the Tempest mini-series, a woman claiming to be Tula enters Garth's life. In truth, it is a doppelganger created by the villainous Slizzath as part of an elaborate plan to siphon Garth's mystical energies for his own dark purposes. Garth sees through the ruse and is able to defeat Slizzath, and finally gain a sense of closure about Tula's death. It is also at this time that Garth adopted a new identity as Tempest.
Most recently, Tula reappears in Teen Titans (vol. 3) issues 30 and 31. Aquagirl is brought back by Brother Blood - along with Hawk and Dove, Phantasm, and Kole - to fight against the Teen Titans. After being freed by Beast Boy and Raven, Kid Eternity is able to lay the deceased Titans back to rest.
Tula has a statue in the "hall of fallen Titans" at Titans Tower, alongside the original Hawk and Dove, Kole, and others.
Lorena Marquez is going on a date at the San Diego Zoo when an earthquake shakes the city and causes it to sink deep into the sea, killing thousands, including Lorena's entire family. She comes into contact with Aquaman, who nurses her back to health, while discovering that she has developed the ability to breathe underwater like an Atlantean.
The two manage to locate the other survivors of the quake, and Geist, the scientist responsible for the catastrophe. They have no choice but to begin rebuilding the city as 'Sub Diego'. When Ocean Master switches lives with Aquaman, Lorena assumes the identity of Aquagirl. After Aquaman exposes Ocean Master's scheme, Lorena keeps her Aquagirl costume, and the two carry on protecting 'Sub Diego'.
In the Titans Tomorrow timeline, Lorena, as Aquawoman, is a member of the Titans. It is revealed that she has developed telepathic powers which she had used to kill (or paralyze) former Titan member Garth.
Aquagirl is a member of the Teen Titans during the events of 52. She assisted Steel in launching an attack on Lexcorp when Natasha was captured by Luthor.