Jarek was the unlucky, rather dimwitted and brutish "last member of the Black Dragon." First debuting in Mortal Kombat 4, he utilized special moves and fatalities popularized by Kano, as well as a Black Dragon Sword, a weapon with sharp, pointy edges that stuck out from the sword's blade. His overall lack of originality has caused him to be labelled as somewhat of an uninspired character by the MK fanbase.
He made his first chronological appearance in Mortal Kombat: Special Forces, where he and other Black Dragon members were freed from a United States Special Forces detention facility along with other Black Dragon members by Kano, who had proposed to reform the Black Dragon clan (In reality, Kano merely wished to use them to slow down any Special Forces agents who may have pursued him in his quest to obtain an artifact called the Eye of Chitian). Jarek was Kano's best student and in Mortal Kombat: Special Forces Jarek was stationed at a downtown office which the clan were using as a front for their activities when he was confronted and defeated by Major Jackson Briggs, and brought back into custody.
Some considerable time later, he escaped to Edenia, only to find himself caught between two fires there: Shinnok and the Special Forces. Reluctantly, he agreed to help his sworn enemies defeat Shinnok. Jarek's short temper, forgetfulness (he seems to not realize that Shinnok is dead, and that the Black Dragon were completely destroyed) and irredeemable bad character would seem to eventually cause his own (literal) downfall. Shortly after the defeat and destruction of Shinnok's forces, he fell from a cliff in an attempt to kill Lieutenant Sonya Blade. Whether he truly died or not will be revealed in time, as he is slated to make a reappearance in Mortal Kombat: Armageddon, with a redesign for his appearance.
Alignment:
Alignment: Evil
Mortal Kombat 4

Believed to be the last member of Kano's klan, the Black Dragon, Jarek is hunted down by special forces agent Sonya Blade for crimes against humanity. With the emergence of a much greater evil, Sonya focuses her strength on the new menacing Quan Chi. Jarek now finds himself fighting alongside Sonya and Earth's warriors to help defeat the evil Elder God, Shinnok.
Mortal Kombat: Armageddon

What was done to me by the Special Forces could only be described as brutality. But that's fine. I can take it. What angered me was that somehow Jax found me. I'd covered my trail, kept to the shadows. But still I was routed out.
Jax dropped me into a ravine, assuming that would be the end of me. It would have been if I hadn't thrust my weapon into the cliff wall to slow my descent. I was badly injured, so I went into hiding. My rumored death would be the ultimate camouflage as I regained my strength.
Obsessed with thoughts of revenge, I traveled all over the realms looking for ancient texts that would show me a fatality worthy of my betrayer. But my injuries made perfecting these new techniques a very painful task. My frustration turned into rage and I no longer cared who had sold me out. I would kill them all ? a sentiment Quan Chi apparently shared.
Quan Chi recognized the carnage I had left behind as I practiced my new fatalities on the good people of the realms. He was impressed and offered to help me increase their power and effectiveness. All I needed do was fight beside the Forces of Darkness in Edenia. The means of enhancing my fatalities would reveal itself, and all my enemies would be there for the slaughter. Soon I'll have revenge. The time will come to finish them all.
Mortal Kombat 4

Sonya: It?s over Jarek! Shinnok is dead? the good guys won. You?re coming back with me.
Jarek: Never Sonya! I agreed to help defeat Shinnok, not turn myself in to the Special Forces. The Black Dragon live on!
Sonya: The Black Dragon died with Kano. You?re the last one Jarek!
Jarek: Never! AAARRRRGGGGGGGGHHHHHH!!!
Sonya: Come in Major Briggs? This is Lieutenant Sonya Blade, WHAAA?
Sonya: AAAAAAAHHHHHHHH!!!!!! (Jarek drops Sonya off cliff)
Jax: Sonya! This is Major Briggs? come in Sonya this is Jax are you there?
Jarek: (Laughing)
Mortal Kombat: Armageddon

The power of Blaze drew chi from all the kombatants and funneled it into Jarek. He suddenly felt as if death itself were guiding his actions. Laughing maniacally, he sealed off the crater and unleashed a storm of fatalities upon his fellow warriors. None could escape the maelstrom of deadly energy. When at last the tempest abated, Sub-Zero's spine lay quivering next to Kano's still-beating heart. An armless Jax knelt beside the two halves of Kung Lao's body. Jarek had finished them all!