Shared movie universe-building is the norm in Hollywood now and Warner Bros./DC Entertainment are very much embracing that approach to franchise construction with the rapidly-developing DC Extended Universe. First, director Zack Snyder's Batman V Superman: Dawn of Justice will introduce several key characters to the DCEU, including a new big screen version of Batman (Ben Affleck), as well as Wonder Woman (Gal Gadot) and Aquaman (Jason Momoa), among others. Certain characters and major events featured in Batman V Superman will then either be referenced by and/or directly affect the storyline in David Ayer's supervillain team-up action/thriller, Suicide Squad, with the latter due to arrive less than six months after Snyder's film hits theaters.
It was previously rumored that Mera, Aquaman's love interest and eventual Queen of Atlantis in the DC Comics universe, will similarly make her big screen debut in the first of Snyder's two planned Justice League movies, before she goes on to play a larger role in the Aquaman solo film currently scheduled for release in 2018. We've now gotten additional confirmation that this is, in fact, the plan and WB/DC has now entered negotiators with Amber Heard (Magic Mike XXL, The Danish Girl) to handle the role of Mera, opposite Momoa as the (eventual) King of Atlantis.
THR is reporting that Heard has entered negotiations with WB/DC to play Mera on the big screen, with the plan being for the character to appear in Justice League Part One first, followed by a larger role in Aquaman. James Wan (The Conjuring, Furious 7) is directing Aquaman and THR also reports that there are two different screenplays for the project currently in development. One of them is being crafted by David Leslie Johnson, who also penned Orphan, co-wrote Wrath of the Titans, and collaborated recently with Wan on The Conjuring 2; the other Aquaman script is being put together by Snyder's 300 movies co-writer, Kurt Johnstad.
It's worth noting that this is actually a relatively common approach, when it comes to the screenwriting process on big-budget tentpoles. Such upcoming movies as WB's The Legend of Tarzan and Universal's reboot of The Mummy franchise were likewise developed in this manner - and the final Aquaman script draft will probably contain what are considered the strongest elements from the two screenplays being written. As to what the actual storyline for the film will be, well, that's another matter.
Director Patty Jenkins' Wonder Woman movie will take place at least partially in the early 20th century, providing what should be some useful backstory for Diana Prince, after filmgoers are introduced to her in the present-day DCEU in Batman V Superman. It's plausible Aquaman will likewise take place before the events of Justice League Part One and provide more information about the shared history between Momoa and Heard's DCEU characters after we meet them for the first time. In addition, the New 52 DC Comics storyline-turned DC animated feature film, Justice League: Throne of Atlantis, may serve as the story template for the Aquaman movie (much like how the Batman: Assault on Arkham animated film appears to be serving as the template for Suicide Squad).
Throne of Atlantis, for those unaware, takes place before Mera has become the Queen of Atlantis and revolves around a storyline that includes the Justice League (as well as Mera) in a major capacity. As such, it would be in keeping with what appears to be the shared universe construction approach on the DCEU to incorporate elements of that film into the Aquaman live-action movie too. That would set the stage for the latter project to explore the romance between Aquaman and Mera with greater depth - at the same time, providing a solid emotional backbone for Wan's comic book adaptation.
Batman V Superman: Dawn of Justice will see theatrical release on March 25th, 2016, followed by Suicide Squad on August 5th, 2016; Wonder Woman on June 23rd, 2017; Justice League Part One on November 17th, 2017; The Flash on March 23rd, 2018; Aquaman on July 27th, 2018; Shazam on April 5th, 2019; Justice League Part Two on June 14th, 2019; Cyborg on April 3rd, 2020; and Green Lantern on June 19th, 2020. The Superman and Batman solo films have release dates TBD.