Obito wore a variety of different masks over the years to hide his identity when he interacted with others.
The most likely reason was to conceal his identity from the viewers. It wasn't until later when fans realized that it was Obito, which could be the reason why he was impersonating another character even when he was alone with Zetsu.
Obito went by the name Tobi after resurfacing prior to the Fourth Shinobi World War. They have similar personalities, and they are also actually voiced by the same voice actor in the English version of the anime. On top of that, Obito wears a mask before the Fourth Shinobi World War that resembles Tobi's face.
Neil Kaplan first voiced Obito's Madara impersonation in the video game Naruto Shippuden: Ultimate Ninja Storm 2, because the CyberConnect2 fighting game's storyline was ahead of the television series. In the game, it is revealed that Obito is not the real Madara.
Declaring that he had nowhere to run, Naruto slams the Rasengan into Tobi's face, shattering the mask with Naruto asking his enemy who he is.
Out of fear of going on a rampage, she jumped in front of Kakashi's Chidori, which killed her. Witnessing the death of the one he loved so much turned Obito into a villain who is primarily responsible for the Fourth Great Ninja War. However, Rin's death was merely a trigger, after which Obito snapped and turned evil.
Obito Uchiha, also known by his iconic alias, Tobi, as well as the Masked Man, is one of the main antagonists of the Naruto franchise. He is the true leader of Akatsuki and serves as a dark reflection of the titular hero Naruto Uzumaki.
Ultimately, the battle is a stalemate and a true testament to Obito's strength. Kakashi is one of the strongest characters by the end of the manga and the show, but Obito is definitely his equal.
Obito Uchiha is, perhaps, the biggest villain in the world of Naruto. Obito became a villain after witnessing the death of Rin at the hands of Kakashi. Convinced that the world of dreams was the way to go forward, Obito did everything in his power to help Madara achieve his goal.
Obito's hate for the Uchiha was simply a result of Madara's animosity towards the clan, as they had betrayed him long ago and had decided to side with the Senju-led government.
When Obito first comes into contact with Madara, he refers to him as his precious forefather. Having Obito say that could mean that he is a direct descendant of the legendary ninja. It does explain the reasoning behind taking up Madara's namesake as his own after becoming leader of the Akatsuki.
Surprisingly, he wasn't given the opportunity as he ended up dying at the hands of Kaguya Otsutsuki towards the end of the Ninja War.
Itachi wasn't strong, he was super smart. Obito feared his smartness. He knew Itachi would destroy any plan of obito as long as he's alive. Obito was not afraid of dying, he was just afraid of his plan getting ruined.
Because he knew the truth that Kakashi didn't kill Rin rather Rin killed herself throwing herself onto Kakashi's Chidori. And he hated Kakashi because Kakashi failed to protect Rin, that's it.
In order to gain access to the other dimension, Madara stole Kakashi's Sharingan, thus stripping Kakashi of all of its powers.
With Naruto Uzumaki, the Seventh Hokage, being considered the strongest of all time, it is quite clear that the weakest of all Hokage is one of Kakashi Hatake and Tsunade Senju.
7 Stands No Chance Against: Naruto Uzumaki
Even someone as strong as Madara Uchiha, or Kaguya Otsutsuki wasn't safe from his explosive power, which just goes on to show that Obito, someone much weaker than those villains, would find himself on the losing end when compared to the protagonist of the story.
In conclusion, Obito Uchiha would defeat Itachi Uchiha when comparing the two characters in their strongest forms. Obito has one of the strongest, if not the strongest, Sage Mode in the series and has enough chakra reserve to beat Itachi.
1) Itachi Uchiha
Undoubtedly one of the most tragic characters in Naruto, Itachi Uchiha shouldered the burden of killing his own brethren to stop a coup d'état in the Uchiha clan, orchestrated by his own father. All this, in order to protect the village.
Madara Uchiha (Japanese: うちは マダラ, Hepburn: Uchiha Madara) is a main antagonist manga and anime character in the Naruto series created by Masashi Kishimoto. He appears for the first time in "Part II" of the manga and the Shippuden anime adaptation, as a major antagonist.
Obito had given one of his Sharingans to Kakashi when his left eye was impaired. Obito was confident that he was about to succumb to his injuries, so he decided to give his eye to Kakashi. In the future, during the events of the Fourth Great Ninja War in Naruto, Kakashi ended up losing his first Sharingan to Madara.
Tobi assisted Itachi in the Uchiha clan massacre, and collected several Sharingan eyes of the dead Uchiha clan members. He must have implanted one of these Sharingan eyes in his left eye socket. During the battle with Konan, he has two Sharingan eyes.
So, around 2,000 Uchiha but no more than that, really. And as my last point: The execution of the massacre. For all we know, Obito's kamui dimension belonged specifically to him and even if one of those uchihas turned out to have a kamui of thier own who says it would bring them back to 'reality'?
Itachi clearly knew that Obito was the true leader of the Akatsuki, and he also knew of and feared Obito's (Sharingan) abilities, hence placing his own Mangekyo Sharingan on Sasuke and setting it so that Amaterasu activated when in the vicinity of Obito's Sharingan.