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Who predicted a background radiation left over from the early universe before its discovery?

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Oval map of the cosmic microwave background radiation from NASA's WMAP mission, showing a mottled pattern of blue, green, yellow, and red representing temperature variations. — Cosmic microwave background A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.

The prediction of background radiation from the early universe was a collaborative effort involving several scientists over many years.

Beginning in 1948, the American cosmologist George Gamow and his colleagues, Ralph Alpher and Robert Herman, calculated that the high temperatures of the early universe would have produced a thermal radiation field. They estimated that this radiation would have cooled to a few kelvins by the present day as the universe expanded.1

In the early 1960s, the problem was revisited by researchers at Princeton University, including Robert H. Dicke and P.J.E. Peebles, who were actively planning a search for this radiation. While these theoretical predictions were being developed, Arno Penzias and Robert Wilson accidentally discovered the radiation in 1965 while conducting experiments with a microwave receiver. The two groups subsequently published their findings on the prediction and discovery of the cosmic microwave background simultaneously.1