According to The Green Lantern Wikia: Nautkeloi is the water breathing Green Lantern from the planet Aeros. Although he was in the Corps for many years, very little is known of the Green Lantern of Aeros. He first met Hal Jordan (Ryan Reynolds) during a Green Lantern conference on the planet Yquem. The Green Lanterns defeated Sinestro (Mark Strong) who had attempted to infiltrate them. The Green Lantern of Aeros served during the Oan/Qwardian Power War, and the Crisis on Infinte Earths.
It isn't clear what role Nautkeloi will play in Martin Campbell's Green Lantern.
Green Lantern was released June 17th, 2011 and stars Ryan Reynolds, Blake Lively, Peter Sarsgaard, Mark Strong, Temuera Morrison, Jenna Craig, Jon Tenney, Mike Doyle. The film is directed by Martin Campbell.