In 1948, Alpher predicted that if the Big Bang theory was correct, there would be a cosmic microwave background radiation detectable throughout the universe. No one paid him much attention, even after Arno Penzias and Robert Wilson discovered the radiation by accident in 1964. Penzias and Wilson won the Nobel Prize in 1978 for their work, but Alpher remained unacknowledged.
Alpher also proved that the Big Bang theory meant that the ratio of hydrogen to helium in the universe would be about 10:1, which is exactly what astronomers observed. His thesis advisor, George Gamow, asked if Alpher would mind having Hans Bethe's name attached to the paper, although Bethe had not worked on the research at all. In his later years, Alpher said he was annoyed by the way that Gamow treated his research almost like a joke, but the fact is that people remember the paper better because it's known as the Alpher, Bethe, Gamow paper. (The paper was published on April 1, 1948, making it seem even more of a joke.)
When I was a kid, reading about Alpher and the Big Bang was one of the things that inspired me to study Physics. I hope Alpher will eventually get the recognition he deserves.
(Washington Post obituary: Ralph A. Alpher; Physicist Published Theory of Big Bang)