In Pokemon Ultra Sun and Ultra Moon, trainers will be able to capture every single Legendary Pokemon that has appeared in previous Pokemon games, from the very first generation to the Generation 7.
Depending on the version that the trainer is playing, the Legendary Pokemon that can be caught will be different. Some Legendary Pokemon such as Giratina require both copies of the game.
Here’s a look at the version exclusive Legendary Pokemon you can catch in Ultra Sun and Ultra Moon respectively:
Ultra Sun: Ho-Oh, Raikou, Groudon, Latios, Dialga, Heatran, Reshiram, Tornadus, Xerneas
Ultra Moon: Lugia, Entei, Kyogre, Latias, Palkia, Regigigas, Zekrom, Thundurus, Yveltal