Although this name looks similar to the old Scandinavian Brandon (from "brand" or sword) its origins are quite different. Brendan is an ancient Irish name; it was originally Breanainn, and comes from an old Celtic (probably Gaelic) word meaning "prince." In modern Gaelic the name is usually spelled Breandan.
There were two 6th century Irish saints named Brendan. The more famous of these was known as Brendan the Navigator or Voyager. It is said that when he had taken holy orders, he prayed to go on a pilgrimage, and was shown a vision of a beautiful island. He set off in a boat to find this place, encountering many magical adventures along the way (including riding on a whale). Eventually he found the island, a kind of paradise based on a mixture of old Celtic and Christian myth. When he returned from his voyage, Brendan went to live near Limerick, and later died there.
There were two 6th century Irish saints named Brendan. The more famous of these was known as Brendan the Navigator or Voyager. It is said that when he had taken holy orders, he prayed to go on a pilgrimage, and was shown a vision of a beautiful island. He set off in a boat to find this place, encountering many magical adventures along the way (including riding on a whale). Eventually he found the island, a kind of paradise based on a mixture of old Celtic and Christian myth. When he returned from his voyage, Brendan went to live near Limerick, and later died there.