Pokémon Platinum introduced Looker, a trench-clad detective whose goal was to foil the plots of nefarious organizations like Team Galaxy and Team Plasma. However, he has disappeared in action for some time; his last appearance was in Pokémon Ultra Sun and Ultra Moon in 2017, and no trace of him was present in either the Let's Go games or Sword and Shield. As the character was introduced during Generation IV, it has been speculated that he could make a return in Generation IV remakes, Pokémon Brilliant Diamond and Brilliant Pearl.
Unfortunately, this is not the case. Looker is once again nowhere to be found in the newly released remakes. This may have something to do with the games that are remakes of Diamond and Pearl versus Platinum, where Looker was first introduced. Interestingly, the remakes feature cosmetics and features from Platinum and beyond that weren't in the original versions of Diamond and Pearl, further adding a layer of mystery to the reasoning behind Looker's exclusion.
That's a bit fitting, given Looker's profession: an investigator who pursues the truth behind many of the evil groups in the Pokémon world. In Platinum, Looker regularly encountered the player's character throughout the game's story and provided updates on his mission to take down Team Galaxy. Towards the end of the game, he succeeded in his mission by arresting the leader of Team Galaxy. Unfortunately, we won't see that mission in remakes.