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. They then became aware of Riker's alien nature and the Minister of Security was contacted. (TNG: "First Contact")
Rivas was portrayed by Jonathan Frakes.
According to director Cliff Bole, "I had a lot to do with Jonathan's look, which was created as a fast concept, and quickly executed by Michael." Frakes himself added, "That was an intense makeup. I got plugs stuck up my nose, and various other things, but it was even more intense after being beaten up. Westmore does great beating up as you can see from Mr. DeNiro." (Star Trek: The Next Generation Makeup FX Journal, p. 80)