If you can't recall what happened in which episode, this might help: http://www.epguides.com/lost/
Best Jack backstory?
Best Kate backstory?
Best Sawyer backstory?
Best Locke backstory?
Best Charlie backstory?
Best Hurley backstory?
Best Sayid backstory?
Best Sun & Jin backstory?
Best Michael backstory?
Best Claire backstory?
Best Boone & Shannon backstory?
Best Eko backstory?
Best Desmond backstory?
Best of the rest?