1.Identity of Vidur as we all know

- As we all know that Vidur was the prime minister of Hastinapur as well as the major advisor to the king Dhritarashtra.
- He was often called as the embodiment of Dharma and the Pandavas had been rescued by Vidur from the cunning plans of Duryodhan and Shakuni in many instances.
But who is Vidur???
- Many years ago a bunch of thieves took something valuable from their king’s palace while he was sleeping and kept them in Rishi Mandavya’s hermitage while he was in meditation.
- After a search operation all the stolen things were collected from Mandavya’s place and the king gave him the insane punishment of impalement.

[Yamamaraja and the sage Mandavya]
- After death he asked Yamaraj about the injustice done to him.
- Yamaraj replied that some insects were impaled by you during your childhood and so that was the cause behind your mode of death.
- Then Mandavya told Yama that his extent of punishment far exceeded his childish sin as an ignorant child.
- Then he cursed Yamaraj to burn in the mortal world in the personification of Dharma as a sudra and to be helpless during the war between Dharma & Adharma in front of you.
- And may be that was the reason why he was born to the maid of Ambalika by sage Vyasa and was appointed as a prime advisor to the king of Hastinapur.
- Eventually when the war was on the verge of commencement,he was helpless for being unable to stop the war because he had not the authority to take any decision regarding the war. At last he resigned from the position.
So we can see that life is all about cause and effects. “When there is a cause,you can’t avoid its effect and if there is an effect,there must be a cause behind it.”
2. When Yudhisthir entered heaven he found all the Kauravas there

Yes you have listened right. It sounds shocking ,right? Well,there is a story behind it. Let’s jump to that story without wasting any more time.
What is the story?
- When the Pandavas along with Draupadi started their journey to heaven one by one died on the way because of their sins except Dharmaraj Yudhisthir accompanied by a dog in the personification of Dharmaraj.
- When Yudhisthir entered heaven,he was shocked to find all the Kauravas there welcoming him. He even shocked more to get to know that his brothers along with Draupadi were in hell suffering their punishment for their respective sins in the mortal world.
Story behind it….
- Actually some generations ago ,king Kuru choose this land(kurukhetra: Land of Kuru) to settle there.
- He performed many yangyas and rituals there for embedding spirituality with the 8 virtues.
- By impressing with this Lord Vishnu gave him a boon that “ Any person dying here doing his/her duty will go to heaven irrespective of other factors”
- As Kshatriya the Kauravas died on that land doing their duty of fighting as warrior. So eventually all of them found themselves in the heaven after their death.
Well,this is the real story.
3.Bheesma: The one and only legitimate heir to the Hastinapur throne

- Well,we all know the story of Mahabharat and its result. In the entire story, all of we are revolved around the Hastinapur throne.
- Sometimes it was Duryodhan and sometimes Yudhisthir. Moreover we fight against ourselves to give resaons for whosoever was eligible for the throne or not.
- I was also shocked and amazed when I got to know about the true fact.
- The fact is that Ganga putra Bheesma was the one and only legitimate heir for the throne of Hastinapur. Let’s rewind from the beginning.
- Bheesma was the 8th son of Hastinapur king Shantanu and Ganga. Then after sometime Shantanu was attracted by the charm and beauty of Satyavati and wanted to marry her.
- So here Bheesma’s vow came into picture to remain celibate for the entire life as Satyavati’s father put a condition before marriage that Satyavati and Shantanu’s son will be the prince of Hastinapur.
- But 2 of their sons Vichitravirya and Chitrangada died early in their life leaving Hastinapur throne empty.
- Here Sage Vyasa came into picture. Vyasa was begeted to Satyavati by Rishi Parasara before marrying to Shantanu.
- So Satyavati requested his son Vyasa to beget his daughter-in-laws.Then Dhritarashtra,Pandu and Vidur were begeted to Ambika,Ambalika and a maid respectively.[NOTE-This was a practice of that time called NIYOGA. Whenever there was a situation of no heir to the throne, because of death of the King, a very pious and pure tapasvi (sage / rishi), who doesn't hold or have even an iota of lust, used to make the queen conceive with one union.]
- Then their lineage continued from Dhritarashtra and Pandu in the form of Kauravas and Pandavas and they continued to fight among themselves for the throne.
- Also another fact is that Even Shantanu was not a Kuru. Bharata lineage was stopped when Bhoomanyu was adopted and made the king of Hastinapur. That was many generations before Shantanu. But considering the time of Mahabharat war,Bheesma was the only legal heir to the Hastinapur theone.
But the fact remains the same that none of them were legally eligible for the throne.
NOTE: All types of comments,suggestions or compliments to improve and modify the answer are welcome.
I will be adding more interesting stories of Mahabharat to my above answer,whenever I find something interesting as well as lesser known.
Thank you for reading.
Special thanks to Thyagarajan KR , Sandesh Balan , Pallavi Alai for their valuable comments for improvement of the answer.
SOURCE:Wikipedia and other internet sites.