Angel is a whisper gnome assassin (Rogue/Beguiler/Swordsage) and one of the main four members of The Party.
At some point before the campaign began, she left the Feywild and joined The Organisation, a shadowy cabal of mercenaries and assassins who covertly resist the Deluvian invasion. She was trained by a mysteirous swordsman until he was killed in battle with a deathfin monitor from the Blood Mountain monastery.
She later joined up with Little One, apparently shortly after he left his mother's cave (as she was the first non-dragon he met). Shortly after this, they encountered Black and Draven, saved a caravan from dire bears and arrived in Corso's Chasm, thus beginning the campaign.
Fighting with a spiked chain and no small amount of guile, Angel is often seen as the least moral of the group, such as when attacking a (apparently) human hostage rather than negotiate. Nonetheless, she is committed to fighting the Deluvians and is loyal to her friends.
She also has a pretty cool suit.