Well, he's almost certainly a God's Knight. His uniform looks more like a God's Knights' uniform than a Admiral's uniform or something else. It's possible that Admirals wore different uniforms back in the day. But, if someone's this close to a Gorosei (and probably Imu themselves possessing that Gorosei at the moment in order to enable the Reversi), I would expect them to be a God's Knight. Imu wants to keep his existence a secret. If he shows himself, he's going to want someone closer to him to back him up, if possible.
And I think it's possible that we've seen this guy before. Because there is ONE God's Knight that we saw back on God Valley who might have been old enough to live this far back in the timeline.
He could be....umm..."Giant Horned Bearded Bat-Winged Devil Guy".
(Chapter 1160)
He doesn't really LOOK similar to this new Smoking Guy. But, Devil-Guy looks like he's on the older side, here. So, he could have been active 24 years before God Valley. The only other God's Knight we know about who could even potentially be a candidate is the Skull-Headed Guy. And he fits this Smoking Guy's build even worse! So, if it's someone we've seen before, I think Devil Guy is really one of our only options.
Although, the more interesting questions might be "Why is this God's Knight HERE, instead of out fighting in the war?"
Maybe Imu just wants a bodyguard around while he's using Reversi on the royal family? That's not impossible. But, I think it's likely that Smoking Guy has a Devil Fruit ability that Imu wants to use on the royal family.
We know that Gunko/Shuri ends up with memory problems later on. So, is it possible that Smoking Guy has Pudding's Memory Fruit? Could Imu have been using this God's Knight's Devil Fruit to brainwash the royal family even more permanently by literally editing their memories?
You know what? I'll even go one step further. The top of Smoking Guy's face is obscured this chapter. Could he be hiding a Third Eye, just like Pudding? Could Smoking Guy end up being Pudding's father?
That's...probably pretty unlikely, to be honest. Oda has been using old Devil Fruits a lot in flashbacks, lately. But, he almost never gives them to similar-looking characters. It would be...VERY "coincidental" for the Memory Fruit to end up with another Three-Eye Tribe member.
But, I do kind of enjoy the potential irony. The Celestial Dragons seem to have been using women for babies and then discarding them. So...then Big Mom manages to kidnap a Celestial Dragon herself, uses him to make a baby, and then discards him, just like they do. It's rather dark, but there is a poetic justice to it, in it's own way. Plus, if Smoking Guy had the Memory Fruit, that would actually explain how and when Big Mom managed to get ahold of such a powerful Fruit.
Let's do some math. Gunko in the present day is 77 years old, and in this current flashback she's 15. Which means this flashback is happening about 62 years ago. Smoking guy...could be any age, really. But, let's assume he's around 30 years old 62 years ago. Pudding was born 16 years ago. There's a 46 year gap between those two time periods, which would mean Smoking Guy would have been around 76 years old back when Pudding was born. That's old...but not impossibly old, to produce a child. It's feasible, if unlikely.
(For the sake of argument, God Valley was 38 years ago, so Smoking Guy would have been 24 years older than we see him here, so he'd be around 54, which kind of tracks, too. So him being Devil Guy also works out okay. It probably can't be both, though, since you can only have one Devil Fruit at at time. So, either he has Memory powers to alter Gunko/Shuri's memories, or he has Devil-Bat powers. Or...something completely different entirely.)
I doubt this is actually the case. And this guy would might be too old for Big Mom, even years ago. But...I could see Big Mom snoo-snooing a old bedridden guy to death. His poor, poor arthritic pelvis.
Again, I'm probably off base here. But, these are my best guesses given the very little information that we have.
