Now it has been revealed that Tobi isin't Madara so who is he? I've got my own theory and I think that Tobi is Kagami Uchiha. Why do I think that, well when Tobi was fighting Konan, his mask broke and a part of his face could be seen
Has you can see, the eye shape is the same. The age would be acurate since Kagami was part of Danzo and Hiruzen's team in the first Shinobi world war making Kagami knowledgeable of Madara since he would have been around when Hashirama and Madara fought.