He was possibly the most powerful of the Rahkshi. Vorahk nearly succeeded in killing Toa Nuva Onua and Pohatu and was partially responsible for the destruction of Onu-Koro. Vorahk can only steal physical strength and energy, not actual powers.
Vorahk was destroyed by the Toa Nuva at Kini-Nui in the final battle against the Rahkshi. He was imprisoned in ice, along with Kurahk. Vorahk was chosen by Teridax to go after the Avohkii because his power is the enemy of Prosperity, the prospect of Onu-Matoran.
currently, Vorahk incredably become one of the vanguards of a new master, Emperor Fang, his evil presents similates the Makuta that he and the other rahkshis obey him without question (Rahkshis don't talk anyway) and now leads an army of non-dark spawnic Vaki.