Klengel was born in Leipzig, and studied with Emil Hegar in his youth. His father was a lawyer and an amateur musician, and was a friend of Mendelssohn. After his 15th birthday, Klengel joined the Leipzig Gewandhaus Orchestra where Klengel played first cello, and began touring in Europe and Russia. Klengel also became a soloist at that point, frequently giving solo performances.
Klengel rose to become principal cellist of the orchestra, aged 22, in 1881. There he remained for over four decades: to celebrate his fifty years of service, Wilhelm Furtwängler conducted a jubilee concert, in which Klengel played the cello part in a double concerto he composed for the occasion. (Wikipedia)