The Shadow Triad is a group of three ninja-like Team Plasma subordinates that are only loyal to Ghetsis. They don't appear to have any feelings, which is evident at N's Castle, when one of them say a bit about N's Playroom, and says that he doesn't feel anything at all when he goes in there. They first appear at Chargestone Cave (where Ghetsis instructs them to protect N) and then in Icirrus City, N's Castle and the Marvelous Bridge. They always appear to lead players on to the next Team Plasma event. They never battle the player and all three look identical.
They make one final appearance in the game after the defeat of Team Plasma; when the player has scoped out the new areas of the Unova region now accessible to him/her, the trio will appear on the bridge leading back to Nimbasa City and inform the player that Ghetsis has gone off to another region to re-think his plans. Before departing, they gift him/her with the Lustrous Orb, Adamant Orb and Griseous Orb - the three items that power up Palkia, Dialga and Giratina respectively. They explain they gave the player these items as it was their master's wish; they depart, wondering what to do as Ghetsis has relieved them of active duty under him after this task.
In the Pokémon Adventures manga, they are shown speaking to Ghetsis.
The Shadow Triad, as seen in the manga.
Their manga appearance is quite similar to the appearance of [w:c:deathnote:Mello|Mello]] from the anime/manga series Death Note.