Who was the person who went on trial for treason and his punishment was to be sent out to sea for the remainder of his life?

The person you are referring to is Algernon Sidney, an English politician and writer who was tried for treason in 1683. He was accused of conspiring against King Charles II and was ultimately sentenced to death. However, his punishment was commuted to transportation, which meant he was sent to the American colonies for the remainder of his life. Sidney's case is often cited in discussions about the rights of individuals and the limits of governmental power.