Officially, Castle and Firefly actor Nathan Fillion is set to appear as "TDK," an original character created for the DC Films universe, in James Gunn's upcoming movie The Suicide Squad. But since before the character was officially named, rumors have swirled that Fillion will in fact play a version of the third-tier superhero Arm-Fall-Off Boy, a minor character who tried out for the Legion of Super-Heroes and didn't make it, but would go on to have more adventures over the years, sometimes using the name Splitter, since the post-Zero Hour reboot of DC's timeline gave some characters new names that were more '90s-friendly.
The character in the comics has the ability to remove his limbs and use them as blunt weapons. They pop on and off more or less like the arms on an old He-Man toy, with a bloodless process that leaves an empty socket for the limb's bone to be popped back into after use.
The tissue designs that co-creator Curt Swan came up with for what his vacated sockets would look like, resemble the emblem on TDK's costume pretty closely, which is why rumors began to circulate that Fillion would be playing the character after early set photos leaked. Gunn decided to deny the rumors. Fillion said that he was fine with fans thinking that he was playing Arm-Fall-Off Boy, since it would prevent him from accidentally blowing the name of the actual character he was playing. He assured fans, though, that Arm-Fall-Off Boy wasn't the name in the script.
Nevertheless, the rumors have kicked into high gear again following yesterday's release of a green-band trailer for The Suicide Squad in which Fillion's character appears to be standing with his arms detached from his torso and floating in the air alongside him. Unless we missed an issue somewhere, that's not a power that Arm-Fall-Off Boy has, but just the idea of someone wearing that logo and being separated from his arms is enough to get Twitter speculating again.
One plausible guess is that the character of Arm-Fall-Off Boy was considered off-limits because of the character's co-creator, Gerard Jones. It is common practice for DC to allow creators to request a payment when their characters are used in other media, and DC has largely avoided making Jones's work available in recent years. The writer, who had runs on Justice League Europe and Green Lantern in the late '80s and early '90s, was arrested in 2016 on suspicion of possession of child pornography, and started a prison sentence in 2018. It's possible that a desire to avoid association with Jones drove the decision to avoid using the character of Arm-Fall-Off Boy, even if the movie's character does appear to be similar. Jones did co-create at least two characters who made it to the big screen recently -- Topaz, who had a supporting role in Thor: Ragnarok, and the Green Lantern character Yalan Gur, who had a brief cameo in Zack Snyder's Justice League.
The appearance of floating arms, separated from his body by a visual effect that resembles Doom Patrol's Mr. Nobody (ironically, Fillion's Firefly co-star Alan Tudyk), raises some questions, as it looks like while his body might come apart, it definitely isn't just by popping things into and out of place manually and utilizing them as blunt weapons. It's still possible he will have similar abilities -- and a lot of fans have speculated that "T.D.K." might be short for the name "The Detachable Kid" -- but it's highly unlikely that they will reveal he is from the 30th Century or anything like that. That's all speculation, though, as is the "Detachable Kid" naming and even just the notion that Fillion is probably playing some variation on the character. Still, it seems like reasonable speculation given the context.