Complex sentence: Albert Einstein (14 March 1879--18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).
Split into simpler sentences: Albert Einstein (14 March 1879--18 April 1955) was a German-born theoretical physicist. Einstein developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).