Sakon and Ukon

and the older brother were twin brothers and the apparent leader(s) of The Sound Four (Orochimaru's bodyguards). To help distinguish between the two, Sakon wore beads around his neck and Ukon had a somewhat deeper voice. Also, their bangs were on opposite sides (Ukon's being on the left, Sakon's on the right).

Personality
Sakon and Ukon enjoyed bad-mouthing the opposition. Orochimaru noted Sakon to be the fastest and strongest member of the Sound Four, traits Sakon was very proud of. When in battle Sakon liked to prolong the fight by toying with the opponent and use unnecessarily powerful techniques. This tendency of Sakon's caused him to slow down the rest of the group whenever he got interested in an opponent. Ukon was able to counteract this flaw by being more impatient and hasty than his brother, forcing Sakon to quickly end his battles.

Invasion of Konoha arc
Sakon and Ukon made their first appearance with the rest of the Sound Four, erecting a barrier to keep others from interfering in Orochimaru's fight with the Third Hokage. They later escorted Orochimaru when he fled.

Sasuke Retrieval arc
The Sound Four escorts Sasuke Uchiha when he decides to join sides with Orochimaru. After Team Shikamaru caught up with the Sound Four, Sakon and Ukon were separated from the rest of the group by Kiba Inuzuka and Akamaru. They almost killed the two, but before they could do so they were stopped by Kankuro. Kankuro, with his puppets Karasu and Kuroari, killed Sakon and Ukon with Black Secret Technique Machine One Shot, saving Kiba and Akamaru.

Abilities
With their kekkei genkai, Soma no Ko, Sakon and Ukon were able to merge with the bodies of others. Ukon generally used this ability to remain within Sakon's body where he could bring out some of his body parts to aid Sakon in blocking or attacking. Ukon can separate from Sakon's body so that the two can attack independently, though he was not used to moving on his own and thus tired easily. The two could heal quickly when merged together.

Like the rest of the Sound Four, Sakon and Ukon had been given a cursed seal. When the second level of their seals were active, they resembled ogres with red skin, longer hair, and a single horn (on opposite sides for each brother). Also, as said by Ukon, he could, while in level 2, deconstruct his body on a molecular level and enter another person's body. At that point he was able to alter the cells and proteins of his target at will, effectively killing them, and then leaving them to reconstruct his own body again. This technique, however, had the disadvantage of him taking the same damage as the body he has invaded, as seen when Kiba stabbed himself in the stomach with a kunai.

While split apart can they use the Summoning: Rashomon by standing at a certain distance away from each other. According to both of them this was their ultimate defense developed by Orochimaru.

Creation and Conception
Sakon was the final member of the Sound Four to be created by Masashi Kishimoto. After struggling to decide who Sakon should fight, Kishimoto decided to have Sakon take part in a two-on-two battle against Kiba and Akamaru. Thus he created Ukon and placed him within Sakon's body so that they could act as one person.