Of all the marine fauna inhabiting the Metkayina reef, only the enormous, highly-intelligent, sea-dwelling tulkun are truly sentient. In fact, the tulkun possess their own names and a rich family history and culture as well as sophisticated music and poetry. Eons ago, the tulkun engaged in long stretches of bloody warfare that spanned generations. Eventually, the tulkun changed their ways and collectively swore to a life of absolute pacifism. With their thick armor plating shielding them from aggressors, tulkun have no need for violent retaliation.

The tulkun share a unique interspecies kinship with all of the various marine reef clans. Each Na’vi is paired with a brother or a sister tulkun calf for life. The Na'vi communicate with the whale-like creatures using a constructed sign language.

The RDA have set their sights on the tulkun after the discovery of a naturally occurring substance in the creature’s brains known as amrita. The substance has the medical power to stop human aging. Since this discovery, the RDA have deployed tulkun hunting squads to capture and harvest the material.