A significant part of the epic Mahabharata narrates rivalry between the princely cousins Kauravas and the Pandavas and the climax Kurukshetra War where Pandavas win over Kauravas.
Kaurava brothers were the 100 sons of Kuru. Pandava , the five sons of Pandu. Draupathi is married to the five brother Pandavas.
As they knew Pandavas can not be defeated in martial power, Shakuni tricks Yudhistra into a game of dice. Shakuni is the wicked character and uncle of Duryodhana the elder of Kauravas.
In a stumble of events Yudhisthira gambles away his kingdom, wealth, his four brothers and Draupathi.
The overjoyed Duryodhana asks his brother Dushasana to drag Draupathi by her hair into the court and strip her cloths, as he is now his property won in the dice game. As they are all now properties of Kauravas the Pandavas bow their head helpless, including the much stronger Bhima. Duryodhana even asks Draupathi to sit on his thigh.
Lord Krishna mystically appears to the helpless Draupathi and gives a boon. Dushasana finally collapses as could not disrobe Draupathi of the inexhaustible clothe. In the scuffle her hair gets untied. She wows to not to tie her hair until it is washed with Dusshasana. Bhima on his part wows to break the thighs of Duryodhana , as he asked Draupathi to sit on his thigh.
As per the condition of the dice game , the Pandavas and Droupathi were send to 14 years in exile, including 1 year in secrete exile.
During this secret period, they live in the court of King Virata. Draupathi disguises herself as the maid of the queen Sushena. Keechaka , her brother was lustful towards Draupathi and troubles her frequently. Draupathi asks help from Bhima , who is now pretending as a cook in the palace.
Bhima advice her to invite Keechaka to meet her in the night. Instead of Draupathi , Bhima waits for him and kills him.
See also Bhima's Gateway , Mythology of Hampi and Gods of Hampi