Complex sentence: In 1951, Johann Brummer joined Damelin as a teacher, in 1952, becoming a partner and serving as Educor's Executive chairman until his resignation in 1998.
Split into simpler sentences: In 1951, Johann Brummer joined Damelin as a teacher. Thereafter, in 1952, Brummer became a partner and served as Educor's Executive chairman until his resignation in 1998.