The Triad

The Triad was the most powerful collective of Upper-Level Demons. Initially appearing to be loyal to the Source of All Evil, they were the considered the leaders of the Underworld after his vanquishment. The Triad has been responsible for most of the attacks on the Charmed Ones. Given their large behind-the-scenes presence in events, they can be considered the series' primary antagonists.

They first became known to the Charmed Ones in 2000, but were killed by Cole Turner soon after when he turned on them. They then returned five years later as the demons Asmodeus, Baliel, and Candor, who were vanquished by the Charmed Ones twice.

Early Life
The Triad has always been the second highest evil in power when the Source of All Evil ruled the Underworld. They worked separate from him, but did his bidding when necessary. However, it was hinted that other demons, such as the Brotherhood of the Thorn, never fully trusted them. Like the Source, they had many demons working for them who they send out to kill the Charmed Ones.

The Rise of the Triad
They first appear in season 3 as male demons, who have full black eyes just like the Source, Belthazor, and Sykes (the latter of whom were both among those they sent to kill the Charmed Ones). They wear long dark red-like hooded robes, with a pentagram on the back. Each of them possess many powers. When they become aware of the existence of the Charmed Ones, they begin sending Demons after them to kill them. When all of the previous demons fail, they order Belthazor, Cole Turner's demon alter ego, to go after the Charmed Ones. Belthazor comes very close in killing the sisters, but falls in love with Phoebe Halliwell, the youngest of the three known sisters at the time, which leads to him killing the Triad.

The Return of the Triad
The Triad reappear in season 8, composed of 3 upper-level demons: Asmodeus, Baliel, and Candor, forming a fitting name pattern of A-B-C. This time, they wear a black robe, with a usually upside-down pentagram on the front of it. They are responsible for kidnapping Christy Jenkins, and hiring demons to guard her and raise her for fifteen years to brainwash her into a killer. Those demons later get vanquished by Christy, her sister Billie, and the Triad, in many separate intervals.

Xar
A demon named Xar, a former member of The Triad, orders a demon to tell the Charmed Ones that The Triad is back, thus exposing them. Xar tricks the Halliwell sisters into going after The Triad, because he doesn't want them to take over the Underworld. The Triad became aware of this and killed Xar.

Battle at Magic School
The Charmed Ones go after them, and battle them at Magic School. In the battle that follows, Phoebe draws Candor away while Piper and Paige battle Asmodeus and Baliel. After Baliel throws a fire ball, Piper freezes the two and has Paige orb Asmodeus in front of the fire ball before unfreezing the scene, vanquishing Asmodeus. With Asmodeus dead, the Triad's power is weakened and Piper manages to vanquish Baliel with three blasts from her molecular combustion power and Candor is forced to flee. Candor later appears before Christy after freezing the Charmed Ones and Billie around her, as he tells her that they taught her everything she knows, and now that The Triad is weakened, she must go forward alone, to reunite with the Ultimate Power, her sister Billie. Candor then leaves, and unfreezes the others. Later on, Candor gets killed by Christy, for being responsible for the death of Christy and Billy's parents.

Return as Spirirts
It is later discovered that The Triad cannot be destroyed as easily as previously thought. Very similarly to the Source, their physical bodies can be vanquished but they continue to exist in spirit form with all their powers until they are strong enough to constitute new bodies for themselves. Therefore, The Triad still exist, but as spirits, they continued to progress their plan to kill the Charmed Ones, with Dumain, who serves them. (This also confirms and explains how they are the same Triad that Cole killed in season 3 resurrected in full). Their spirits later get vanquished by the Charmed Ones, using the power of the Hollow.

Final Vanquish
However, Dumain went back in the past with Christy to warn the Triad of their death, though as he was warning them, The Charmed Ones and Billie arrived from the future as well, and vanquished the Triad, once and for all. They proceeded to vanquish Dumain and Billie vanquished her sister Christy.

The Triad

 * The Triad is a collective of powerful upper-level demons.
 * Virtual Emperors of the Underworld, when together, the
 * powers of this evil cabal increase exponentially and there
 * is no known method of vanquishing them. Though
 * unconfirmed, rumours persist of splinter groups seeking to
 * carry out their own agendas.

Powers and Abilities
As demons of the highest level, comparable to The Source, Zankou and most powerful high level demons, they are highly resistant to most manners of attack, and all their abilities are extremely powerful, though the Charmed Ones are among the few magical beings whose attacks can actually harm and weaken the Triad. In addition to this, their power works as a collective, much like the Charmed Ones, stronger with all three alive. Weakened, they were more vunerable as shown when Piper was able to vanquish Baliel with molecular combustion after Asmodeus was vanquished when before it likely wouldn't have worked.

Appearance

 * First Members: This Triad wore dark-red, hooded robes with a gold pentagram on the back. Their eyes were completely black, indicating their power level.
 * Asmodeus, Baliel, and Candor: Unlike their previous forms, this Triad wore black robes without hoods and with an upside down pentagram on their chest. Their eyes were normal, human eyes.

Trivia

 * The most glaring continuity error in the appearances of the season 8 Triad was the pentagram on their robes not always being upside down. This is most likely the result of costume and editing oversights in production.
 * Asmodeus is the name of a demon from the Ars Goetia, the first section of the demonology book The Lesser Key of Solomon. Here, he is described as a King and governs seventy two legions of inferior spirits. Other names taken from this are Andras, Barbas and Shax.
 * Asmodeus is also present in other religions and mythologies. He is described as a King of Demons, one of the Seven Princes of Hell and a demon of Lust.
 * Baliel was the name of a Biblical demon.
 * It was revealed the name of the three triad members are Asmodeus, Baliel and Candor. It's also a coincidence that a demon who was helping of them, with hopes of becoming a triad member name was Dumain, which is all alphabetical order.