Simplify the following text for a Grade 6 native English-speaking person.
Original: Sarah Siddons ( 5 July 1755 â `` 8 June 1831 ) was a British actress , the best-known tragedienne of the 18th century .
Simplified: Sarah Siddons ( 5 July 1755 -- 8 June 1831 ) was a British actress . She was the best-known actress who played tragedies of the 18th century .