If so he beat Brendan to it, who is supposed to have pulled off that feat in the 6th century, well after Merlin.
Merlin, a.k.a. Ambrosius Aurelius, was actually a Briton of Roman descent. He became king, uniting the Britons against the invading Anglo-Saxons. And later he was consigliere and general wizard to his successor King Arthur. Then he became keeper of the Holy Grail, and finally sailed to Avalon.
http://www.grahamphillips.net/Merlin/merlin2.htm
So then Ambrosius Aurelius discovered America before Brendan, who was before Leif Ericksson, who was before Christoforo Colombo...
But I'm confident Ambrosius Aurelius will have to hand over the laurels of the discovery of America to at least the Phoenicians if not earlier types. Like the Solutreans!
