Complex sentence: In 1982, he returned to the US to found the bank's syndicated leverage finance group, which constituted the origins of the investment banking business at Chemical and later Chase Manhattan Bank, which he ran until the merger with J.P. Morgan & Co. in 2001.
Split into simpler sentences: In 1982, he returned to the US to found the bank's syndicated leverage finance group, which constituted the origins of the investment banking business at Chemical and later Chase Manhattan Bank. Lee ran the investment bank until the merger with J.P. Morgan & Co. in 2001.