akanehatake
people im sorry but obito is UTTERLY DEAD so tobi isn't obito tobi si MADARA UCHIHA and from what i have read madara fought the 4th hokage at one point so there you have it
whee it's not the 4th Hokage but the 1st Hokage.. and Uchiha Mandara was actually defeated by the 1st Hokage of which became the means of which the two of them actually creating the Konoha village ..
Tobi being Uchiha Mandara was actually reveal on the current chapters of the manga... when Jiraiya infiltrated the Hidden Rain village ... that's Chapter 370
Kakashi Gaiden started in Chapter 239 and ended in Chapter 244 in the manga
Kakashi Gaiden.. tells us that Kakashi developed Chidori at a young age and when he got the Sharingan .. that's the time he perfected the jutsu.. it also gives us a first hand look on the 4th Hokage