Who was Jarasandha who attacked Mathura 17 times

Who was Jarasandha-

King Kansa had two queens-Asati and Kriya, which was the daughter of Jarasandha of Magadha. After Lord Krishna was killed by Kansa, both of his father went to Jarasand. Jarasandha attacked Mathura 17 times for revenge. Shri Balram and Shri Krishna each time slaughtered all his army and left him alive.

In the 18th time, he invaded Mathura with the Kalyavan of received from the Goddess of being invincible. Lord Krishna sent Vishwakarma to Dwarka, already sent all the Mathuravasi to Dwarka.

Running in front of Kalyavan, Shri Krishna came in a mountain cave and put his answer on the sleeping king Mukchand. Coming from behind, Kalyavan stabbed Mukchand by thinking of Krishna and then Kalyavan was consumed by the sight of Mukchand.

Mukchand aid of Indra defeat to Rakhyasa, and  Indra give a blessing to Mukkundwhoever would wake him forcibly, would be consumed only after seeing his vision.

Then slaughter Kalyavan's army - after coming in front of Jarasand, Shri Krishna and Balram escaped to the Brabasan mountain. Jarasand set fire to the mountain. Shree Krishik Balram went to Dwarka along the way from Akhma. Understanding Jarasand that both were burnt - went on playing the sting of their victory.