Rivas Jakara was the alias taken by Commander William T. Riker while working undercover on Malcor III while working as advance scout in preparation for a possible First Contact scenario between the Malcorian government and the Federation. According to the identity created for Riker, Jakara was a merchant from the Marta community on Malcor III.
Riker was surgically altered to look like a Malcorian. This included altering his cranium so he would exhibit the enlarged forehead typical of the species. However his digits were not modified, which made them distinct from the webbed fingers displayed by the Malcorians.
While disguised as Jakara, Riker was severely injured and taken to a medical facility. There, Berel, the physician in charge, became aware of Riker's alien nature and the minister of internal security was contacted. (TNG: "First Contact")