Madara is most definitely strong, at least strong enough so that all the other villages have to form an alliance. Madara is in all aspects the main enemy in naruto and he is seen to be feared by even the most respected ninja.
Uchiha Madara
I believe it is Madara Uchiha because after he killed Konan, he took rinnegan from Nagato and transplanted it into himself. He almost is as strong as the Sage of 6 Paths.
Uchiha Madara is a really strong shinobi from the Uchiha clan. Not the guy with the orange mask. The guy with the mask says he is Madara but he is Uchiha Obito. Madara awakened the rinengan and that is why he didn't die early. Obito would have been dead but Madara found him and saved him. Then Madara entrusted his plans to create a better world to Obito and died. Check out naruto manga 599-608
Tobi is Madara Uchiha who is very powerful. He has the eternal mangekyo sharingan and also the power to control the nine tailed fox. The fox said to sasuke that Madara Uchiha is really strong.
He didn't become Madara, he is Madara.
James Madara goes by Jamie Madara.
Madara was stronger than Itachi by default. Remember that sometime near the end of his life Itachi became ill. If they ever fought, Madara would have probably won especially due to the reasons that Itachi had some kind of illness, and naturally low stamina by default. Madara is extremely strong, having survived a death blow and living this long.
Madara.
Madara!!!!!!!!
Madara is not Tobi.
kisame assumed madara was the fourth mizukage , after all fourth mizukage yagura was actually manipulated by madara/tobi ... so you can assume that madara was the real mizukage and yagura was just a puppet ...