Jack of Harts

The Peloran were the first aliens to make open Contact with us. Though they were obviously watching Earth for some time. They understood Earth languages and cultures going back for centuries and longer. And many speculate they walked throughout the streets of Earth as they did so. Some of them could pass for an Earthborn human even when under medical examination. Though they would have completely confused a Pre-Contact genetic history test. Short of that, the Peloran that made Contact could have disappeared on Earth and never been discovered.