Answer
Aung San Suu Kyi, the leader of the National League for Democracy (NLD), was the main rival of Thein Sein in the 2015 general election in Myanmar. Suu Kyi, a pro-democracy activist and Nobel Peace Prize laureate, had been under house arrest for many years and was released in 2010. The NLD won a landslide victory in the election, marking a significant shift in the country's political landscape.