( The N in this name is pronounced like 'n' in 'on'. The 'DH' is pronounced like a hardened sound of 'th' in 'brother')
Jaraasandha was the ruler of Magadha country. His father was Brihadratha.
Jaraasandha was very strong. He was born dead as two halves to his mother. The parents threw the pieces out side the fort walls. A demoness named Jara(Jara was the name of a hunter too, who hit Krishna in the end to kill him. Do not get confused with the names.), tried to eat them by clubbing the two pieces. Soon after being joined, the pieces forged to each other and the baby got life. He was hence called Jaraasandha (=joined by Jaraa ). Jara gave the boy to their parents.
He gave his two daughters Asthi and Praasthi, in marriage to Kamsa, Krishna's uncle. Since Krishna klled Kamsa, Jaraasandha grew feud with Krishna and attacked him seventeen times with 23 akshouhinis. He lost each time except in the last time when Krishna fled with all his men to Dvaaraka.
Also, he stood for Shishupaala in his attempt to marry Rukmini, whom Krishna forcibly took away at the request of the bride herself.
Thus he was an arch rival of Krishna.
Before the paandavas begin their raajasooyam sacrifce, Krishna, Arjuna and Bheema went to Jaraasandha. Bheema fought with Jarasandha for 15 days and killled him.
Jaraasandha's son Sahadeva ( not to confuse with paandava Sahadeva) fought on the kouravas side.
Once Karna defeated Jaraasandha in a hand-to-hand fight on the occasion of Duryodhana's abducting the daughter of the Kalinga king in her svayamvaram.
"After praying to Naaraayana, Nara, Sarasvathi and Vyaasa, then one should read the Jayam."
DEDICATED TO MY DEAR NIECE VYSHNAVI KRISHNA