1 ) Vidura was half-brother of Dhritarashtra and Pandu. He was born via Niyoga between one maid Parishrami and Maharishi Vyasa. He couldn't be ruler of Hastinapura due to his birth status because he was son of one maid.
2 ) Vidura became Primeminister of Hastinapura.
3 ) Vidura was respected via Lord Krishna and all other nephews which were Yudhisthira, Bhima, Arjun, Nakula and Sahadev.
4 ) Vidura forewarned Pandavas many times and rescued them from Duryodhana's plots. It was Vidura who had warned all Pandavas regarding Duryodhana's plans to burn them within Lakshagriha.
5 ) Vidura was incarnation of Lord Dharma and was born within humans because of curse of Mandavyamuni.
6 ) Vidura was married to Sulabha one lovely maiden who was child of King Devaka one of other kings who ruled near kingdom of Hastinapura.
“King Devaka had one daughter endued with youth and beauty and begotten upon a Sudra wife. Bringing her from her father's abode, Bhishma married her to Vidura of great wisdom.”
-Mahabharata.
7 ) Vidura had many children which is written within Mahabharata but names of those are not listed.
8 ) Vidura was wise and Vidura Neeti is his excellent narrative which he narrated to king Dhritarashtra.
9 ) Vidura had one bow called Govardhana bow which Sri Vishnu presented to him and it was more powerful than Gandiva bow of Arjun.
10 ) It was Vidura who protested before Draupadi's Vastraharan with Vikarna but had to keep silent when Duryodhana called him ungrateful. It was Vidura who told Yudhisthira not to play dice with Duryodhana. But his efforts were within vain.
11 ) Vidura had said that one blind man (Dhritarashtra) cannot be king which wasn't liked via his brother Dhritarashtra.
12) Vidura invoked Sage Sanatsujata because Dhritarashtra wanted some answers to questions of his about life of his sons.
13 ) When Duryodhana insults Vidura he went away from Hastinapura and he had then undertaken pilgrimage to many places and had taken dip within many holy rivers.
14) When Lord Krishna became peace messenger and came to Hastinapura wicked Duryodhana wanted him to stay within his palace and then finally try to switch him to their side and not his brothers. But Lord Krishna instead went to Vidura's humble place and ate simple meals which Sulabha had made for him with her sincerity and her love.
15) Vidura wanted to side with Yudhisthira within Mahabharata war which he did and also gave resignation as one of Hastinapura's ministers.
16 ) When Dhritarashtra's sons were slayed within war Vidura felt pity for him and he respected his brother once again and forgot what they had said to each other before war.
17) 21 years after Yudhisthira was king, Dhritarashtra with Queen Gandhaari decided to retire to forests and Vidura also wished to go with them. Yudhisthira tried to prevent them but they blessed him and then went to forests to end their lives. Vidura met his end while he meditated one day. When sad Yudhisthira came within that forest and went little near to that body Vidura's soul merged into Yudhisthira which proved that both Vidura and Yudhisthira had been manifestations of Lord Dharma. One celestial voice told Yudhisthira not to cremate his uncle's body. That's why Yudhisthira leaves body of Vidura within those forests and returns to Hastinapura.
