Mera grew up as princess of a undersea civilization in another dimension, where all people have the power to control water and make simple water constructs by solidifying the water. After her parents' death, she was made queen. After a time not specified, the throne was usurped by a would-be conqueror named Leron, who took control of Mera's realm of Xebel and sentenced her to death, forcing her to flee through a dimensional warp created by Xebel's main scientist. From there she came into Earth's Atlantic Ocean, where she met Aquaman and Aqualad, who helped her battle the usurper and regain her throne.
Although separated from her savior by a dimensional barrier, Mera could not forget the man who gallantly helped her regain her throne, and fell helplessly in love with Aquaman. When she learned that the machine that opened the dimensional rift between her world and Earth would only open a rift one more time before breaking, and that making another would take many years, she chose to go to Earth and find her true love. She talked to her people before she left, and they understood and let her go.
At that time, Aquaman had just been crowned king of the Atlantean city Poseidonis and was required by law to take an Atlantean woman as his bride and queen. When Mera saved the city from Oceanus (a rebel from her own world who had followed her to Earth) she was made an honorary Atlantean citizen. She married Aquaman in the largest and most magnificent ceremony that Atlantis had ever seen, including the guest-appearances of Aquaman's land-locked friends, the Justice League of America.
Shortly thereafter, Aquaman and Mera had a son, Arthur Curry Jr., who inherited his mother's power to solidify and control water. They became Atlantis' most beloved and charismatic royal family, but nevertheless a tragedy struck them: in a confrontation against Black Manta, Arthur Curry Jr. was killed. The ramifications of this act were hard for the couple. After time, though, even this tragedy was surpassed, and they returned to live as a inseparable couple once more. As of Arthur Curry Jr.'s death, however, Aquaman left the throne and Atlantis to seek revenge.
At some point, it was discovered that Mera would die if she continued to live on Earth, for the vibrations of this plane of existence were to tearing her body apart. She was exiled to her dimension to live there seemingly forever, away from her husband. But her body was taken over and cured of this strange factor by the woman chosen to rule after Mera's departure to Earth, V'Lana. V'Lana came to Earth to learn how to gain control over the fish of Earth, as her realm had no fish. The fish would become V'Lana's army and allow her to gain control over her entire dimension. But V'Lana's plans were thwarted by Aquaman and Mera (whose consciousness was still in her body, she could only send telepathic messages). Then Mera came back to Earth, to live happy forever with her husband.
From this point, though, begins Mera's downfall at the hands of the awful Keith Giffen, whose ramifications brutally affect today's Aquaman series by Peter David.
In the 89's mini-series, Atlantis is invaded by aliens while Aquaman is absent. The ruler is Mera, who is rapidly losing her mental health (to the point where she is committed to a mental asylum). There she languishes until Aquaman returns to free his people, a task made more difficult when Mera, now completely insane and convinced that the death of her son was Aquaman's fault, escapes and tries to kill him. Failing, she manages to conjure up a dimensional rift that allows her to return home.
After this, she was seen in Aquaman's 1992's series, where she was shown in another dimension married to Thanatos, a former Aquaman's foe, believing he was Aquaman. She had a son, who she believes to be her killed son, Arthur Curry Jr. Recently, she has appeared in the Peter David's series, and it looks like Thanatos managed to completely control her mind, and (retconning by LG here) Thanatos may have been behind Mera's mental disintegration in the Giffen series, too. She eventually returned to Thanatos's half-world to be with and protect her son, AJ, whose father has been left unspecified.
Mera has the power to solidify water, forming it into various shapes, which she controls telepathically. Mera can summon forth waves to give her propulsion, making her at least 4 times faster than Aquaman, although without her power, she can swim almost as fast as Aquaman. She can breathe underwater, and her body's natural density, which allows her to survive undersea pressures, gives her some degree of super-human strength and damage resistance, as well. In one story only, it was told that she could make a dimensional rift to travel to her own dimension.
Mera has a vulnerability: if her skin is coated with a handful or higher amount of lead, she loses her powers.
Mera is a truly sensitive and caring individual. She will go out of her way to help those in need, even at the risk of her own life. She was one of the rare silver-agers females (and by rare I mean I remember only one other - Hawkwoman) who was not a truly "I will do anything to annoy the hero" supporting female cast member. She was not the "female in need of rescue" kind of character, like Lois Lane and Iris West and Carol Ferris etc. She had a personality and, from time to time, she saved Aquaman with her own powers and intelligence. She was not inferior to the main character of the book. She was the voice of reason against Aquaman's hot-headed temper, and sometimes it took Mera's soothing yet commanding voice to bring him out of his reveries.
-Mera Bio by Rodrigo Mariath Zeidan