Simplify the following text for a Grade 10 native English-speaking person.
Original: George Herbert Leigh Mallory ( 18 June 1886 -- 8\/9 June 1924 ) was an English mountaineer who took part in the first three British expeditions to Mount Everest in the early 1920s .
Simplified: George Herbert Leigh Mallory ( June 18 , 1886 - June 8\/June 9 1924 ) was a British mountaineer who took part in three expeditions to Mount Everest in the early 1920 's .