Angel Bob

Angel Bob was a name the Doctor gave to the Weeping Angel that was within the vault of the Byzantium. It was called such because it spoke using Bob's central nervous system and vocal chords to 'speak'. (DW: The Time of Angels)

Before the crash
The Weeping Angel lay patiently waiting and feigned being in a 'dormant' cycle. As it planned, it passed from one private hand to another until it would eventually come in possession of a temporal core to help revive its bretheren. The opportunity came when it came to be stored in the Byzantium.

In the meantime, River Song was sent on behalf of the Church to find it and neutralise it. She managed to get on board the Byzamtium during her investigation and captured four seconds of footage of the Angel. Prior to departing the ship she warned its captain the ship would not reach its final destination.

The Angel caused the Byzantium to crash on an Aplan -killing all passengers but itself- temple on Alfava Metraxis, whose species were wiped out by Weeping Angels in the mid 47th century. The dormant and weak Angels within the catacombs beneath the temple began to awaken and regenerate.

The Angel on the screen
The Angel was able to project itself through a 4 second looped recording shown by River Song to the Doctor, Amy Pond, and Father Octavian.

Amy Pond, alone with the angel and through observing (and not observing) the Angel noticed that it was able to move from within the recording, and was able to stretch its influence beyond the image; deadlocking the doors of the pod, trapping Amy within. The Angel was able to project itself beyond the image and was able to become a projection in the room, however Amy was able to exploit an glitch in the recording allowing her to turn off the projection of the image when it was close to making contact with her. (DW: The Time of Angels)

In the catacombs
The Angel escaped the vault of the Byzantium and went through the Maze of the Dead. When Clerics Christian and Angelo were sent to investigate the further catacombs the Angel broke their necks, utilising their central nervous systems and vocal chords to lure other clerics to their deaths. The last cleric left alive Bob it also removed his central nervous system and vocal chords as a means to communicate with the Doctor, Amy, River and the remaining clerics. The Doctor, upon hearing the Angel use Bob's voice decided to call it "Angel Bob". (DW: The Time of Angels)

Within the crashed Byzantium
After cornering the Doctor and the clerics within the crashed Byzantium "Angel Bob" revealed to the Doctor that the Weeping Angels were no longer just feeding on the ship, and was amused that the Doctor could not see what they saw: a a crack in time. (DW: Flesh and Stone)

As the crack expanded "Angel Bob" attempted to coerce the Doctor into throwing himself into the crack in order to seal it, saving the Angels and potentially Rive and Amy. When the gravity on the Byzantium failed "Angel Bob" and the rest of the other Weeping Angels on board fell into the crack, sealing it. The Angels themselves were subsequently erased from existence. (DW: Flesh and Stone)

Personality
"Angel Bob" showed no remorse for the killing of several clerics and also claimed to enjoy doing it when it spoke to the Doctor using Cleric Bob's vocal chords and central nervous system. It also tormented Amy with a copy of its self by making her think she was turning to stone. The Angel was also very patient and clever; the Doctor guessed it had never been dormant but had rather allowed it self to be captured so it could get the needed power to revive its people.

It also possessed a sadistic sense of humour as it pretended at first to be Cleric Bob before casually saying it wasn't and it had snapped the man's neck to use his voice. (DW: The Time of Angels)