Rajkumari Draupadi

She was the daughter of Maharaj Drupad. She was born from fire from a Yagya. Her twin brother was Rajkumar Drishtadyumn. She was married to the Pandavas. She was calm, polite and friendly but also fierce and angry. She was the most beautiful woman in all of Aryavat.

Rajkumar Drishtadyumn

He was the son of Maharaj Drupad. He was born from fire from a Yagya. His twin sister was Rajkumari Draupadi. He was friendly to his friends. He aimed to kill Dronacharya. His favourite weapon was the sword.

Rajkumari Shikhandini

She was the eldest daughter of Maharaj Drupad. She was a great warrior and also took the form of a man later. She was the reincarnation of Rajkumari Amba. Her favourite weapons were whip and sword. She aimed to kill Bhisma.

Maharaj Drupad

He was the King of Panchal and father to Panchali, Drishtadyumn and Shikhandini. He was fierce and a good warrior but arrogant. His best friend was Guru Dron but they became enemies for a while.

Gandharraj Shakuni

He was the son of Maharaj Subala and Maharani Sudarma. He was an extremely intelligent, crafty and devious man. He influenced his nephews, especially Duryodhan, from their childhood and plotted against the Pandavas multiples times. His favourite weapons were his dice since he was an expert in the game.

Simdhunaresh Jayadratha

Jayadratha (Sanskrit: जयद्रथ) was the king of the Sindhu Kingdom. He was married to Dushala, the only sister of the 100 Kaurava brothers. He was the son of king Vridhakshatra. His son's name was Surath.

Rajkumari Rukmini

Rukmini was the princess of Vidarbha. She was the incarnation of Mata Lakshmi. She was the daughter of King Bhismaka and Maharani Shuddhamati. Krishna heroically carried away Rukmini, as per her wish, and eloped with her as they loved each other and to prevent her unwanted marriage to Shishupal arranged by her brother Rukmi. She helped Krishna in establishing righteousness in Aryavat. (And many more...)

Rajkumari Satyabhama

She was the daughter of Satrajit and was wedded to Krishna. Satyabhama is described to be an avatar of Bhudevi, the earth-goddess who is a Form of Goddess Lakshmi. She aided Krishna in defeating the demon Narakasur. She was best friends with Krishna's other friends like Arjun and Draupadi.

Other ashtabharyaas

Rajkumari Bhanumati

She was the princess of Kalinga and was married to Duryodhan who forcefully abducted her in her swayamvar. She was the daughter of Kalinganaresh Chitrangada. She was intelligent. Bhanumati has a son Lakshmanakumara and a daughter, Lakshmanaa. It is described that Duryodhana loved her immensely.

Rajkumari Amba, Rajkumari Ambalika, Rajkumari Ambika

They were the princesses of Kashi. Bhisma had abducted them on their swayamvar by force and defeated anyone who opposed him. Upon reaching Hastinapur, Ambika and Ambalika consented to marry Vichitravirya, while Amba told Bhishma about her love for Shalva. Learning about her feelings, Bhishma sent Amba to the Saubala Kingdom. But Shalva rejected her. Since Bhisma too was not willing to marry her, she vowed to be the cause of his death and ended her life. Later she reincarnated as Shikhandini. Ambalika and Ambika attained widowhood in their early married life and had to go through Niyoga to get children.

Rajmata Satyavati

Satyavati was the adopted daughter of a fisherman chieftain, Dashraj and was brought up as a commoner on the banks of the river Yamuna. She helped her father, Dashraj, in his job as a ferryman and a fisherwoman.
She married Santanu on her father's condition that their children inherit the throne, denying the birthright of Shantanu's eldest son (and crown prince) Bhishma. After Pandu's death, Satyavati went to the forest for penance and died there. While Satyavati's presence of mind and far-sightedness is praised, her unscrupulous means of achieving her goals and her blind ambition have been criticized.

Hidimbi

She is the Queen of a Rakshasa tribe and sister to Hidimba. She is the wife of the Bheem and mother of great warrior Veer Ghatotkacha. She meets Bhima in the 9th sub-Parva when the brothers were trapped in Kamyakavana. She is also referred to as Bhuṭanadevī (भुटनदेवी) or Pallavī (पल्लवी).

Guru Drona

He was a friend of Guru Sukracharya, the guru of Asuras, including Mahabali. He was the son of rishi Bharadwaja and a descendant of sage Angirasa. He was a master of advanced military arts, including the divine weapons or Astras. He loved his son Ashwadhama very much.

Mahamahim Bheeshma

He, also known as Devavrata, was the eighth and only surviving son of the Kuru King Shantanu and the river goddess Ganga. Originally named Devavrata, he was made the heir-apparent of the kingdom. However, he ceded his rights for his father's happiness and took the vow of lifelong celibacy. Because of this terrible oath, he came to be known as Bhishma and was blessed to live as long as he wanted. He played a major role in the political affairs of the Kuru kingdom.

Bhagavan Parashurama

Born to Maharshi Jamadagni and Renuka, Parashurama was foretold to appear at a time when overwhelming evil prevailed on the earth. The Kshatriya class, with weapons and power, had begun to abuse their power, take what belonged to others by force and tyrannise people. Parashurama corrected the cosmic equilibrium by destroying the Kshatriya warriors twenty-one times. He is married to Dharani, an incarnation of Mata Lakshmi. He is also the Guru of Bhishma, Dronacharya and Karna.

Kulaguru Kripacharya

He is the son of Śaradvān and Jānapadī, born in a particularly extraordinary manner. He is the grandson of Maharshi Gautama. He is a descendant of sage Angirasa. He along with his sister Kripi was adopted by King Shantanu. Later he was accepted as Kul Guru of Hastinapur. It is believed that he was an amshavatar of Brahma.

Ashwadhama

Ashwathama or Drauni is the son of Guru Dron and the grandson of the sage Bharadwaja. He was friends with both Pandavas and Kauravas. He was born with a gem on his forehead which gives him power over all living beings lower than humans; it protects him from hunger, thirst, and fatigue.
His favourite weapons were bow and arrows and sword.

Mahamantri Vidur

Vidura was born through Niyoga- between sage Vyasa and Parishrami, a handmaiden to the queens, Ambika and Ambalika. - when the queens were scared of Vyasa during Niyoga. He is the Prime Minister of Hastinapur and also the uncle of Kauravas and Pandavas. Vidura is held to be a paragon of truth, dutifulness, impartial judgement and steadfast Dharma. He is considered the embodiment of the inner consciousness.

And other Mahabharat characters which I hadn't mentioned yet...
Do keep in mind that the introductions given are the briefest introduction for readers who aren't much familiar with Mahabharat.