Complex sentence: He was elected to the Philadelphia City Council in 1951 and served there until 1958, before becoming the first black judge to be appointed to the city's Court of Common Pleas in 1959.
Split into simpler sentences: He was elected to the Philadelphia City Council in 1951 and served there until 1958. Alexander became the first black judge to be appointed to the city's Court of Common Pleas in 1959.