Learn a Word: Protagonist

A post yesterday featured the song "Seasons in the Sun" by Westlife. The lyrics got me interested and therefore I consulted Wikipedia for some background. There, it is summarized this way:

"The song is a dying protagonist's farewell to relatives and friends."

So, here is a little quiz: What is a protagonist?

Cheers,
Surfer_Diver
2013.9.14