Complex sentence: Later, he was one of the founders of the National Renewal Alliance (ARENA), of which he became President in 1972, and remained a leader in Juscelino Kubitschek's government and President of the National Congress.
Split into simpler sentences: Later, he was one of the founders of the National Renovating Alliance (ARENA), of which he came to be President in 1972. He was still a leader in Juscelino Kubishek's government, and President of the National Congress.