Hoover was an orphaned harbour seal pup picked up and raised by fisherman in Maine (Cundy Harbor Maine on May5 1971). After Hoover became too large, he was donated to the New England Aquarium in Boston, Massachusetts. When he began to become sexually mature, Hoover began to make speechlike sounds. By 1978, at the age of seven, an incredulous observer wrote in the aquarium files "he says 'Hoover' in plain English. I have witnesses". Unfortunately, Hoover died in 1985.
Why is vocal learning in seals important (or, why should a scientist care about a talking seal)? A short answer is here
For more detail about Hoover, see: Ralls, K., P. Fiorelli, and S. Gish, Vocalizations and vocal mimicry in captive harbor seals, Phoca vitulina. Canadian Journal of Zoology, 1985. 63: p. 1050-1056.
There is also a web page on Hoover at the New England Aquarium: Hoover Page
Here are some recordings of Hoover (made in 1981 by Katherine Ralls, and some time later by Terrence Deacon):