According to Antonio Ribera, in his book 'UFO: contact from planet Ummo,' the Ummites are the inhabitants of the planet Ummo. It revolves around a binary star called Wolf 424, fourteen light years away from us, in the Virgo constellation (and not in the Draco constellation as some mention). In the late 40's they received radio transmissions from Planet Earth and decided to come and investigate. They landed in Spain, somewhere in the 50's. In 1965, they contacted a few selected individuals. By now, they supposedly established several bases all over Earth.
Chuck Robers claims the Ummites are of Lyran /Pleiadian descent and are members of the Federation of Planets.
(Note that Iummo is another name for the star Wolf 424 around which the planet Ummo is supposed to revolve).

Some researchers believe that the whole Ummo story was a hoax, or, more correctly, a research project into human paranoia, set up by a Spanish psychologist, Jose Luis Jordan Pena. Or at least, that is what he claimed.
There are, however, quite a few inconsistencies in his explanation. After he made hia claims, it was revealed that he also was not aware that many scientists in Russia had received letters. And when questioned about the topics discussed in the letters, he clearly lacked the required knowledge to have written them. Most researchers therefore reject his claims that he was the author.

On the Internet I found this information on Antonia Ribera and the Ummites:

"Antonio Ribera tells in UFO: Contact from Planet Ummo, of his contacts with a group of beings from the planet Ummo who arrived in 1950, established bases, and acclimatized themselves. In 1965 they began to make contact with twenty people in Spain. Most of these people had some openness to the possibility of extraterrestrials, for they all belonged to group called The Society of Friends of Space. The Ummites said they also had contact with other groups all over the world.
They claimed that in 1948 they picked up a strange radio signal which they were unable to decipher. They eventually traced it to this solar system. The actual transmission had occurred in 1934 and had taken fourteen years to reach their planet, later Earthly investigations confirmed that the transmission had occurred.
The Ummites were surprised at there being intelligent life on this planet and decided to investigate this civilization. They first landed in La Javine in Les Basses Alpes in France. The landing was unobserved and an investigative party of four men and two women was left on Earth.
The Ummites told Antonio Ribera that their planet orbits a star astronomers refer to as Wolf 424 which is fourteen light years from Earth. The planet Ummo is quite similar to Earth. The Ummites are extremely telepathic. They very much believe in the existence of the soul and in a Creator God. At the age of 13.7, Ummite children leave their families for teaching centers where they are prepared for adult life. They make practical use of at least ten dimensions of reality and are aware of far more. They say one of the reasons they are able to travel such far distances in such a short time in their spacecraft is that they use folds and warps in the space continuum. They have sophisticated technology, and their craft can exceed the speed of light. Although similar to humans in appearance, one marked physiological difference is that their fingers are very sensitive to light and other forms of radiation. For this reason they find it difficult to use light switches and electrical apparatus of all kinds.
It was in 1967 that the group in Madrid began to receive an extraordinary member of phone calls and letters from the Ummites on Earth. They hired a typist to type all the letters and told the person they were Danish doctors. When the typist became uncomfortable with the content of the letters, the Ummites produced a tiny sphere, just an inch or so in diameter. This sphere was placed in midair, and as the typist looked into it he saw a scene that had occurred the preceding day when he had been at home with his wife. There was no logical explanation for how this could have been done unless the Ummites were telling the truth about themselves.
They eventually opened bases in eight other countries. Researchers have received over one thousand seven hundred forty pages of written material from the Ummites in Spanish and French and over six thousand in all languages combined. Their ships have been photographed six different times with scores of witnesses of each sighting. Landing tracks have been found on the ground, and metal artifacts have been recovered.
I am grateful to Antonio Ribera for recoding this information in UFO: Contact from Planet Ummo.
(Source Of Information: Hidden Mysteries, by Dr. Stone, 5252 Coldwater Canyon, #112, Van Nuys, Calif. 91410, (818) 769-1181. )"

Original source of the above information was the now defunct, as well as Dr. Joshua David Stone's Hidden Mysteries.