There have been many notable Irish people throughout history. After Ireland's conversion to Christianity, Irish missionaries and scholars exerted great influence on Western Europe, and the Irish came to be seen as a nation of "saints and scholars". The 6th-century Irish monk and missionary Columbanus is regarded as one of the "fathers of Europe", followed by saints Cillian and Fergal. The scientist Robert Boyle is considered the "father of chemistry", and Robert Mallet one of the "fathers of seismology". Famous Irish writers include Oscar Wilde, W. B. Yeats, Samuel Beckett, George Bernard Shaw, Bram Stoker, James Joyce, C.S. Lewis and Seamus Heaney. Notable Irish explorers include Brendan the Navigator, Sir Robert McClure, Sir Alexander Armstrong, Sir Ernest Shackleton and Tom Crean. By some accounts, the first European child born in North America had Irish descent on both sides. Many presidents of the United States have had some Irish ancestry.