Aquaman is the DC Universe underwater super-hero. Created way back in 1941, he started out protecting the oceans from Nazis. He's continued fighting evil to this day, sometimes in his own book, sometimes not, always trying to do what's right for the oceans of the DCU and for the people of Atlantis.
Aquaman, born as Orin to Queen Atlanna and the mysterious wizard Atlan, was abandoned on Mercy Reef as a baby because of his blond hair, which was seen by the superstitious Atlantean as a curse, The Mark of Kordax (The Atlantis Chronicles #7). Raised first by dolphins (Time and Tide), then by a lighthouse keeper who gave him his own name, Arthur Curry (The Legend of Aquaman), you could say he had an unusual childhood. Sometime in his teens he met and fell in love with an Inupiat named Kako. He left (was driven away) before he knew she was pregnant with his son (Time and Tide, current series).
He discovered his Atlantean heritage by dropping in on an oppressed Atlantis, and becoming a prisoner. He learned the language and who his mother was during that time, as well as forging a lasting friendship with Vulko, an Atlantean scientist (The Legend of Aquaman).
Sometime later he was introduced to hero-hood by the Flash (Time and Tide). He didn't like it much, but eventually learned to deal with it, as evidenced by his eventual leadership of the Justice League (not retconned out yet, so we'll say it still happened).
He also was able to claim his birthright as King of Atlantis, though he was surprised to discover that Vulko had led the overthrow of the oppressive religious regime, inspired by Aquaman (The Legend of Aquaman). He met Aqualad, who became his friend and almost-son. He married Mera, a queen from another dimension, and had (another) son with her. Life was going great! (Pre-Crisis DC)
Then, of course, came the bad times. He lost his son to a vindictive Manta, and lost the trust of Aqualad at the same time (Adventure Comics #452). After rocky times, starting with Aquaman's quest for revenge on Manta and ending with his absence when his city was attacked and conquered (Giffen Mini-series), Mera left him for her own dimension. His people slowly lost faith in him, and too eagerly followed his son into disaster (current series). And he even lost his hand, too (current series, issue #2).
In madness and grief, he was slowly brought back into the world of heroes by Dolphin and Aqualad. After learning the secret of Poseidonis, he fought off an alien invasion by uniting Earth's underwater heroes against them. He met his father, Atlan, and learned more about his mystical heritage (current series, issues #1-25).
And then he went mad after his dolphin mother was killed by a Japanese dolphin hunter seeking revenge. He lost control of his powers, which he learned were more formidable than he suspected. He endangered the world enough for the Earth Elemental, Swamp Thing, to step in and wake him up (current series, issues #26-33).
After finding himself again, he asked the sea life to forgive him, and accept him again as their King. In his insanity, though, the sea had fled to the protection of Poseidon, and he had to fight Poseidon's son Triton to regain his status. When he won, a ticked off Poseidon gave him the power of a god to show him that he can't handle it (current series, #34).
Blind, he stumbled onto Animal Man and helped him out (current series, #35). He learned how to control his sonar abilities and to reach into "The Clear" with Animal Man's help. He then returned to his home in time to greet his returning people, who had to get used to living on the surface of the ocean (current series, #36).
But Triton wasn't done with him. After killing Atlan and Poseidon, Triton killed Aquaman and took over the city. Aquaman, in the mythical underworld of Hades, saved Poseidon and returned to life, defeating Triton with Poseidon's help. (current series, #45-46). Then Aquaman went off to another dimension to save Mera, returned and exiled his son Koryak, and had a birthday party.
What happens next is anyone's guess...
The following is the Aquaman entry from "The Great Superman Book," chronicling some of the earliest meetings between Aquaman and Superman. (Note: "S" refers to the indicated issue of "Superman" comics and "Act" refers to "Action Comics." Names in all capitals in the body of the entry indicate and separate entry exists under that name elsewhere in the volume.)
AQUAMAN. A costumed super-hero, gifted with the power to make sea creatures obey his commands, who is the product of a union between a lighthouse keeper and a young woman of ATLANTIS.
In July 1960, after Clark Kent has been swallowed by a whale while on an expedition to photograph marine life for the DAILY PLANET, Aquaman rescues Kent from his predicament so that Kent will not be forced, by rescuing himself, to betray the fact that he is secretly SUPERMAN (S No. 138/3: "The Mermaid from Atlantis!").
In January 1961, at the request of Superman, Aquaman assumes the fictitious identity of MENTAL MAN as part of the Man of Steel's scheme to apprehend the "ACE" RUGGLES gang (Act No. 272: "Superman's Rival, Mental Man!").
In October 1961, after an overzealous agent for the Internal Revenue Service has declared Superman delinquent in his income taxes in the amount of $1,000,000,000, Aquaman scours the ocean for the world's biggest oyster to produce the world's largest pearl (S No. 148/3: "Superman Owes a Billion Dollars!"). (See BRAND, RUPERT.)
In November 1963, when Clark Kent is in imminent danger of drowning after an encounter with red KRYPTONITE has temporarily robbed him of his super-powers, it is Aquaman who finds him and carries him to Atlantis, where "a new form of artificial respiration" is used to save Kent's life (S No. 165/2: "The Sweetheart Superman Forgot!"). (See SELWYN, SALLY.)
Later in the volume: The following is quoted from page 105, entry for Jor-El
By July 1964, while patrolling the sea bottom, Aquaman has retrieved the Kryptonian "record playback machine" and "video-recording" which Jor-El had originally affixed to the exterior of the rocket that carried his infant son to Earth. Narrated by Jor-El, the recording recounts his efforts to decide which of six distant planets would make the best home for his son Kal-El by feeding available data in a "great computer-forecaster." According to the computer-forecaster, young Kal-El would ultimately become a famed lawman and hero on whichever of the six planets he grew to maturity, but the type of hero he would become would depend on the type of planet chosen as his home, so that if he grew up on the water-world of Valair, for example, he would develop into a seagoing hero like Aquaman. As a result of these and other inquiries, Jor-El decided his son would be happiest living on Earth. (Act No. 314: "The Day Superman Became the Flash!").
(Great Superman Book quotes provided by Richard Duncan)
This is a very rough timeline of Aquaman's main titles, starting from the beginning and working up until now. For now, Justice League adventures are left out.