Lets just draw out the timelines of how Madara fought Hashirama that led to his demise and then from then on we can speculate how he is surviving the defeat; how he met Nagato (we all know pre-teen Nagato was trained by Jiraiya); gave him the rinnegan and formed Akatsuki; how he could have snuck in and acted to release the Kyuubi to cause havoc to Konoha (was he already dead because he wore the Tobi mask?); and during the Uchiha massacre, was it him that led to Itachi to slaughtered his own clansmen? (how old was Sasuke when it happened? because the Kyuubi incident happened during Naruto's birth); how Orichimaru/Kabuto seemed to know the existence of Madara dead body?