Obito Uchiha is a major villain in Naruto, responsible for many of the events that kickstarted the series. Designed as a foil to the titular character, Obito's story shows what could have happened if things had gone differently for Naruto. Overall, Obito is a dynamic character with many different facets to his character, but there is one interesting detail about him that most fans may have missed.
Most of Obito's time spent on panel has him hiding behind a mask, mainly because he is posing and acting as Madara Uchiha. There are three different masks he can be seen wearing, and each one has the same basic design: covering his entire face, save for a hole on the right side through which Obito's Sharingan can be seen. The first mask he is seen wearing is orange and features a swirl pattern. The second mask has a tan hue and features nine shapes on it. The third mask is white and is designed in the style of the Sharinnegan, where each tomoe represents an eye hole.
The interesting thing about all of these masks is that each one represents an important aspect of what is going on during the current arc. The orange swirl mask represents the spacetime Kamui jutsu, which Obito is first to use. The second mask (technically the first, chronologically speaking) with the nine shapes is seen during the nine-tails attack flashback arc. Each one of the nine shapes represents one of Kurama's tails. The third and final mask with the tomoe represents the final sequence of the series, the Divine Tree and Infinite Tsukuyomi. The bottom two tomoe are eye holes for Obito to see through, but the third one is positioned on his forehead, where the Sharingan is seen opening up on characters like Madara and Kaguya.
In the grand scheme of things, this detail is incredibly minor but that doesn't make it any less interesting. As a matter of fact, it makes going back for a Naruto reread more fun because each mask is a tease of what's to come, and as it was mentioned above, Obito is the one who put many of the series' major events in motion, so it's fitting that he's the one to don these masks.
Naruto features a wide range of villains but not all of them are as fleshed out as Obito. This interesting detail in Naruto just adds more to his character and to the series as a whole.