Who discovered America, and when?

Though officially the Italian explorer Christopher Columbus "discovered" America in 1492, some scholars have claimed it was discovered up to 700 years earlier.
In what is said to be more than a legend than a fact, the first person who laid claim to discovering America was a sixth-century Irish monk called Saint Brendan. Saint Brendan did exist, but there is no evidence to suggest that he ever made it to the Americas.
There is evidence, however, to show that Vikings visited the Americas—Newfoundland, in Canada—numerous times in the tenth century. They didn't settle there because the American natives were so hostile towards them.
According to Gavin Menzies and a small number of other scholars, the Chinese explorer Zheng discovered the East Coast of America and parts of South America in 1421. This is a controversial view and one its opponents say is based more on hearsay than fact.