Rivas Jakara was the alias of a male Malcorian from the Marta community on Malcor III in the 24th century. This person had known major genetic differences from Malcorians and was under the care of a Doctor Crusher. He had a surgically altered cranium to exhibit the enlarged forehead typical of the species and wore special gloves to give the appearance of webbed fingers. His digits were not modified.
The alias, traveling as a tourist, was used by Commander William T. Riker in 2367 while working undercover on Malcor III. He was sent there as an advance scout in preparation for a possible first contact scenario between the Malcorian government and the Federation. The cosmetic differences were actually procedures done by the Federation.
While disguised as Jakara, Riker was severely injured in the riots that had occurred and was taken to the Sikla Medical Facility. There, Berel, the physician in charge, checked on Jakara's story and found no Doctor Crusher nor a credible description of his home address. The then became aware of Riker's alien nature and the Minister of Security was contacted. (TNG: "First Contact")