Anime:
In anime, the Trio first appears in the first part of SS. The Trio members used to be animals, but were turned into humans do follow Neherenia and Zirconia's orders. The Trio is to find the Pegasus in dreams. When they take the dream mirrors from people, they count to three and a wall appears. The captured person is then tied to the wall and the mirror is taken. Zirconia finally kills them when they start to get nice.

 Manga:

     In the manga, they are created from animals by the AQ. Also, the Trio get killed separately by the Sailor Senshi.

 Chracters:

     Ok, here's some 411 on the separate members of the Trio:

Hawkeye:

Hawkeye likes to attack old women unlike the other members of the Trio because they like to go after young girls. Hawkeye once tried to trick Usagi's mom, so that he could get her dream mirror. Hawkeye has red hair.

Tigereye:

When going after Pegasus, Tigereye goes after the young, beautiful girls because he assumes that Pegasus hides in their dreams. From that, you can tell that he goes after the girls. Tigereye has yellow hair.

Fisheye:

Fisheye is my favorite of the Trio. He's actually kind of funny when he dresses up as a girl to get Mamoru's dream mirror. Then, Diana (Luna and Artemis's daughter) scares him away because fish are mainly afraid of cats.