In "The Wheel of Time Companion" his level of strength in the One Power is described as ++4, making him one of the most powerful channelers known, but the weakest of the male Forsaken in terms of raw channeling capability. Nevertheless he was still above the vast majority of channelers in the current age. His skills as a cunning manipulator, an exceedingly skilled general, and a blademaster offset his relative weakness in the Power amongst his peers.
Little is known of Duram Laddel Cham before he turned to the Shadow, although his skills indicate that he was a powerful force for the Light. Called The Envious, he was a master swordsman and manipulator. He was an advocate and a friend of Lews Therin Telamon. Together, they revived the ancient and forgotten art of swordfighting, and fought together against the Shadow before his jealousy of the Dragon drove him to swear his soul to the Dark One. Later Be'lal's mastery of manipulation earned him the name Netweaver. It is also mentioned that he once played a game of stones with Lews Therin and won and that he always boasted of that. 
During the War of Power he and Demandred led massive attacks in the areas where the Choedan Kal were built, but failed to retrieve the access ter'angreal. He was probably among those who razed the Hall of the Servants in the war.
After his escape from the Bore, he soon adjusted to the political scene of the new world, and maneuvered himself into the position where he could pose as a High Lord of Tear under the assumed name of Lord Samon, effectively ruling Tear in all but name.
A more skilled manipulator than Rahvin and more deadly than Sammael when dealing with enemies in open combat, he planned to lure Rand al'Thor, the Dragon Reborn into the Stone of Tear. He wanted Rand to take possession of (and thus release the seal on) Callandor, so he could then take it for himself.
While hiding in the Mountains of Mist, just before Shadowspawn attacks the camp, Perrin is visited in his dreams by several Forsaken, one of them clearly Lanfear, and then dreams of a meeting of Be'lal and Rahvin in a place resembling The Ways.
Perrin is unable to overhear what they're saying, but their gestures make clear there is mutual dislike and that Be'lal and Rahvin are arguing fervently. When a third man appears, possibly Ishamael, Be'lal and Rahvin briefly appear to take the same side against Ishamael, but soon their short alliance breaks.
During the capture of the Stone of Tear, he fought Rand with a dark heron blade sword made from the One Power. He used the Power as a secondary asset, mostly overcoming Rand with highly advanced swordsmanship - that of a true blademaster. He seemed disappointed that Rand was not yet as good as Lews Therin had been, and Rand was saved by Moiraine Damodred who killed Be'lal with balefire, though Be'lal's intention was not to kill Rand, and he was likely safe from any sort of mortal wound. Forever burned away from the Pattern, he is now out of reach even for the Dark One.
Be'lal is likely a reference to Belial, one of the seven princes of Hell in Christian and Jewish apocrypha, or it could be related to Ba'al, another of the seven princes. The word "belial" in Hebrew describes someone who is extremely wicked or iniquitous.