Lilith

Once human, Lilith was turned into one of only six Sirens, a group of people with unbelievable powers who have been touched by alien technology. She comes to Pandora in search of another Siren, in an effort to find out more about herself.

Gameplay
Lilith is essentially the mage of the group, using her Siren powers to support the group and attack the enemy. Lilith could also be treated as the rogue of the group with her Phasewalk ability turning her invisible for a short time allowing her to sneak around, her Assassin skill tree giving her more melee/critical damage and her Controller skill tree giving her the ability to daze.

Her Elementalist tree adds bonuses for weapons that employ static, incendiary, and corrosive damage. IGN recently released a video showing her using her phasewalk and coming out of it where she blasted enemies flying. It also displayed her other abilities.

Active Ability

 * See Article: Active Abilities for info.

Lilith's skill is called Phase Walk, which lets her turn invisible to enemies (but not teammates), move much faster, and cause a damaging shockwave upon entering and exiting. Gearbox co-founder Randy Pitchford describes it as "kind of like when Frodo puts on the ring, except that when she takes it off she can kill everything around her with a shock wave nova effect."

Skill Tree Calculator
Check out the skill calculator at the official Borderlands site

Trivia
It is possible that Lilith is named after a demon in Semetic mythology, who was believed to be Adam's first wife. This demon is believed to be an extremely beautiful female demon that inhales the life from infants. Other versions of the legend say she was a bringer of disease, illness and death. According to semetic mythology, Lilith gains power every time her name is spoken.