Simplify the following text for a Grade 8 native English-speaking person.
Original: John Russell , 1st Earl Russell , KG , GCMG , PC ( 18 August 1792 -- 28 May 1878 ) , known as Lord John Russell before 1861 , was an English Whig and Liberal politician who served twice as Prime Minister of the United Kingdom in the mid-19th century .
Simplified: John Russell , 1st Earl Russell , KG , GCMG , PC ( 18 August 1792 â `` 28 May 1878 ) was an English Whig and Liberal politician . He served twice as Prime Minister of the United Kingdom in the mid-19th century .