aided Duryodhana in marrying & Defeating

Karna aided Duryodhana in marrying the princess of Chitragandha. In her swayamvara, the princess rejected Duryodhana, who subsequently carried her away by force. The other kings present at the swayamvara pursued Duryodhana. However, Karna defeated them singlehandedly. The defeated included

1. Jarasandha, 
2. Shishupala, 
3. Dantavakra, 
4. Salya and 
5. Rukmi. 

As a token of his appreciation, Jarasandha gifted Karna a portion of Magadha. Bheema defeated Jarasandha with the help of Krishna but it was Karna who defeated Jarasandha earlier singlehandedly. Karna was the first one to expose the weak point of Jarasandha about splitting him in two.