Seaenchai is a Thai Muay Thai fighter who has won the Lumpinee Championship title, which is widely considered the most prestigious title in Muay Thai, in four different weight divisions, while mostly fighting larger opponents. He is considered by many to be the best pound for pound Muay Thai fighter, and is regarded as one of the best fighters of all time. Saenchai would often give up weight to find worthy opponents in Thailand, and from 2003-2014 only lost two times in Thailand when the weights were equal, with all other losses happening when he was forced to have a weight disadvantage to make the fights more evenly matched.
Check out his best techniques against bigger opponents here: