Mother Teresa's greatest achievement was founding the Missionaries of Charity in 1950 in Calcutta, India. It started with 12 members and has grown to over 4,000 members worldwide. She was born in Skopje, Macedonia and joined the Sisters of Loreto as a nun in 1928. From 1931-1948 she taught school in Calcutta, but was deeply impacted by the city's poverty. In 1948 she received permission to work among the poorest in Calcutta's slums, which led to founding the Missionaries of Charity.