Although there was some displeasure over The Grand Inquisitor's look, the first trailer for Obi-Wan Kenobi was spot on. The score alone has fans excited for the series, but that wasn't the only reason for excitement. A young Luke Skywalker made an appearance, along with a famed, but never-before-seen Star Wars location. On top of that, there appears to be a plethora Inquisitors making attempts to hunt down Kenobi. As for the famed Jedi Master, he looks broken and faithless, as he should following the Great Jedi Purge; however, that doesn't mean that Obi-Wan Kenobi will stay broken, especially if he receives help from an unexpected friend -- Captain Rex.
There are tons of rumors and theories about various characters returning to the fold in the Kenobi series, and Captain Rex feels more than likely now. While it's not confirmed, there was a figure in the Kenobi trailer that resembles the popular clone, even though he is only there for a second and seen from behind.
At the 1:08 minute of the trailer, there's a shot of a droid and a stormtrooper. Then, there's a shot of someone's backside at the 1:09 mark. The quick cut makes it look like part of the droid at first, but it's likely not. It appears to be faded, white armor, but because of differences in the design, it can't be a Stormtroopers' armor.
As seen in the image above from the trailer, it has a rounded butt-plate and indentations in the upper-leg armor. Meanwhile, in the picture below, it clarifies what a Stormtrooper's armor looks like on the left, while the right is what Clone Trooper armor looks like. Between these two images, it's clear the armor in the trailer matches the Clone Trooper armor.
If this is for sure Clone Trooper armor in the trailer, theorists can narrow down who it is since Obi-Wan Kenobi is set in 9 BBY -- 10 years after the Fall of the Republic. As The Bad Batch showed, Clone Trooper armor was decommissioned and phased out very quickly, so there's only a few rebellious clones who would still be wearing an archaic set of armor. Theoretically, it could be Wolffe or Gregor, but Captain Rex would make more sense, given his affinity with Anakin and Obi-Wan during the Clone Wars. On top of that, the hint of blue in parts of the armor further denotes that it belongs to Rex's 501st armor.
The last time fans saw Rex was in The Bad Batch, when he helped Clone Force 99 remove their inhibitor chips. Then, Rex went off to continue defending the Republic. He didn't elaborate on what that meant, but it probably had something to do with the very early stages of the Rebellion, so him making contact with Obi-Wan, or at least contributing to the series, would make a lot of sense.
To see if Captain Rex appears in Obi-Wan Kenobi, watch the series' premiere on March 25, on Disney+.