Who was Galileo Galilei?

Galileo Galilei was an Italian scientist whose inventions
and work did much to Renaissance thought in Europe.  He is most famous for his work on
creating a telescope that was usable for astronomical purposes and for his contention
that the solar system centered around the Sun rather than the
Earth.

Historically (as opposed to scientifically)
speaking, Galileo is most important for the fact that he was one of the first to
challenge the Church and other accepted authorities and to, instead, try to find truth
through observation.  This was an important change because it marked a move toward a way
of thinking that was based on science and on observable proof.  This new way of thinking
was to change the world, helping to bring about such things as the Age of Exploration
and even, eventually, the Industrial Revolution.

Galileo,
then, is important both for his specific discoveries and for his contributions to
changing dominant ways of thought in Europe.