Both Andy Lau and Louis Koo acted as 'Yang Guo' in the hit HK drama The Return Of The Condor Hero. Andy take on the role in the 80s and Louis reprises it in the 90s. A famous chinese period novel written by Jing Yong. Yang Guo is considered a golden role in this period drama and the male lead usually shot to instant stardom after playing it. Andy and Louis never look back since.
The real reason why Louis Koo has been maintaining dark tan skin is because he doesn't want to wear too much make up during filming and this allow him to have more rest time.
Andy Lau is married to a Malaysian beauty queen and they have a daughter.