Selim Bradley is the first homunculus Pride. He poses as the adopted son of King Bradley, and has control over shadows.
Selim's background varies between the first anime series and the manga/Brotherhood. In both adaptations, Selim is the son of Fuhrer Bradley.
First Anime Series
Here, Selim is the biological son of Bradley who is completely unaware of his father being the homunculus, Pride. Appearing late in the series, Selim is entrusted with the remains coming from Bradley's former human life which he calls his 'treasure'. Walking in on his father's fight with Roy Mustang, the Fuhrer becomes weakened from his remains being in close proximity of him. In a rage, Bradley kills his son by strangling which allows Roy to get the upper hand on the Fuhrer by repeatedly setting him ablaze by using his human remains as a medium to do so.
Manga/ FMA: Brotherhood
Selim is the adopted son of Bradley in the manga and the anime remake, Brotherhood. Here, Selim is the homunculus known as Pride, the first created by Father despite his young appearance and the highest ranked among them in authority. He first takes action by taking control of Al's armored body to lure Ed into a trap with aid from Gluttony. They engage in battle with Ed, Greed, Darius, Heinkel, Fu and Lan Fan where Selim consumes Gluttony to boost his power. With the battle becoming increasingly risky with Selim gains the upper hand, he gets sealed in a dome of earth with Al by Hohenheim. This doesn't keep Selim trapped for long as he uses Ed's helmet to communicate Morse code by banging on it to signal for Father to bring in Rolf Kimblee.
With his alchemy, Kimblee is able to free Ed and Selim from their earthly prison resulting in Ed having to battle both enemies while empowered by a Philosopher's Stone. The arrival of Tim Marcoh to heal a heavily injured Heinkel evens the odds and causes Kimblee and Selim to flee. With Kimblee dying from injuries he sustained in that battle, Selim absorbs Kimblee to further raise his power.
Selim later appears to activate a transmutation circle with Roy Mustang as a sacrifice for human transmutation. The two appear in Father's lair as he prepared to activate the Amestris Nationwide Alchemy Circle. However, Selim was left very weakened from using his Philosopher's Stones for the transfer to Father's lair to the point where he has difficulty in battling both Elric brothers before Father restrains them for his plans. When those plans backfire, Selim finds himself battling against Ed. Realizing his body is rapidly deteriorating, Selim attempts to take control of Ed's body to preserve himself. However, he winds up being taken over by a Philosopher's Stone-powered Ed instead and finds himself defeated at Ed's hands.
Abilities (Manga/ FMA: Brotherhood)
Besides the standard regenerative abilities that homunculus have, Pride has control over his shadow which he can use to ensnare, control or slice apart his enemies. The shadow gives him limited omnipresence as he is capable of observing the activities of anything that occurs within the Amestris Nationwide Alchemy Circle. He can also absorb the abilities of anyone that he absorbs within his shadow. As long as there is a light source, Selim is capable of extending his shadow long distances which can be stopped if there's an immense amount of light or darkness in the area he occupies as it impossible for a shadow to be cast in such circumstances.