As per Narada and Vayu Puranas, Draupadi was composite Avatar of Goddesses Shyamala (wife of Dharma), Bharati (Wife of Vayu), Sachi (wife of Indra), Usha (wife of Ashwinis) and hence married their earthly counterparts in the form of the five Pandavas. Enraged at a jest by Parvati and the four goddesses, Brahma cursed them to human birth. Parvati thought of the solution wherein they will be born as one woman, Draupadi and hence share the earthly body for a smaller period of time. Draupadi's characteristic fight against injustice reflects Parvati or her Shakti, Kali inhabiting Draupadi's mortal flesh at times. At other times, Draupadi was docile and even waited to be rescued (as in case of Jayadratha and Jatasura) showing the qualities of other goddesses like Sachi and Usha. Other times, she showed astuteness in hiding their true identity and asking Vayu putra Bhima to kill the evil Keechaka like Goddess Bharati would. another explanation, At Pandavas residence Lord Krishna took Draupadi aside and said, "This awkward situation you find yourself in is of your own making. In your previous birth you had pleased Lord Shiva with your prayers. He granted a boon to you. You said that you wanted a husband and to ensure that your request was heard, you repeated it five times in all. Shiva then said that in your next life you would have five husbands." Some sources have a slightly different narration. Draupadi made her request only once but she added a long list of qualities that she wanted in her husband. Shiva said that it would be impossible to find one man with all these qualities. Hence she would have five husbands in her next life. All of them together would posses the qualities she had enumerated. Lord Krishna said ," You will spend one year with each husband. Others will be forbidden to enter the chamber in which you and the husband-of-the-year are staying. If one does so, even accidentally, he would be exiled for one year."
There is one interesting story where it is said that draupadiji prayed and asked for a boon saying that she wants husband which is strongest among all, he should be follower and savior of dharma, he should be smartest , he should be most active and there was no person on earth who had all these qualities hence god gave her boon that she will get her husband but she should accept her in whatever form he comes she has to accept it and she agreed to it, so god gave her 5 husband with different qualities. At beginning when it happened she objected but lord krishna showed her previous life visually and where in she saw that she had given words to god in return of the boon which god had given her. As she was vachanbad she had to fulfill her words. To understand Mahabharata you need to read about past of each and every individual
