1 ) Mandodari was one celestial nymph called Madhura who once came to Kailasa to see Lord Mahadeva and Mata Parvati. Parvatidevi had been to one of her son's place and meanwhile the nymph Madhura set her eyes on Lord Mahadeva and she saw him with love. Mata Parvati returned that time and coincidentally saw Madhura set her eyes on her husband which made her wrathful. She cursed Madhura that her maiden beauty will vanish and she would be ugly. Madhura became one frog and Mata Parvati threw her into one well. Lord Mahadeva has pity on Madhura and tells her that after 12 years she would be free of the curse and she would be beautiful as she was back then. After 12 years the frog becomes Madhura and she was within the well. She calls out for some one who could help her come out of that well. Mayasura and his wife the celestial nymph Hema did penance to be blessed with female child (They had two sons who were Mayavi and Dundubhi). They came to the well when they listened to one female voice and found Madhura. They helped her come out of the well. They are pleased because the celestials had blessed them with one female child. They make her their child and name her Mandodari.
2 ) When Ravana once comes to Mayasura he sees Mandodari and tells her father to marry her to him. Ravana is one powerful ruler therefore Mayasura marries his child Mandodari with Ravana.
3 ) It is believed that Mandore place with Jodhpur is the native place of Mandodari and she and Lankapati Ravana married there with each other.
4 ) Between the five elements Queen Mandodari is equated to water who is ‘turbulent on the surface and deep within her spiritual quest.’
5 ) Mandodari was the loved one of Ravana and chief Queen of Lanka.
6 ) Queen Mandodari knew about the power of Lord Vishnu and advised Ravana not to do sins and not to touch women without their wish.
7 ) It is said that Mandodari was the mother of Sita within many Puranas but Valmiki Ramayana doesn't mention that Mandodari is the mother of Mata Sita. Mata Sita mentions to Anusuya about her that she is Ayonija (one who is not born from her mother's womb). This means Mata Sita was not the child of Mandodari and she is really the child of Mata Bhumi.
8 ) Mandodari was humble and kind.
9 ) Wicked Ravana wanted to slay Mata Sita but it was Mandodari who stopped him from this sin.
विवृत्य नयने क्रूरे मुष्टिम् उद्यम्य दक्षिणम् || ५-५८-७४
मैथिलीम् हन्तुम् आरब्धः स्त्रीभिः हाहा कृतम् तदा |
“Rolling his cruel eyes and lifting his fist, Ravana was about to kill Seetha. Then one alarm was raised by women there.”
स्त्रीणाम् मध्यात् समुत्पत्य तस्य भार्या दुरात्मनः || ५-५८-७५ वरा मन्द उदरी नाम तया स प्रतिषेधितः |
"Springing up from the midst of those women, a royal woman named Mandodari the wife of that evil-minded Ravana, ran to him. He was restrained because of her."
10 ) When Lord Hanumana went to Lanka to search for Mata Sita he noticed one lovely woman within the palace of Ravana who was sleeping peacefully and he had mistaken her for Mata Sita but he came to know that it could not be Mata Sita because how could she be peaceful when she was away from her Lord Rama? From this Lord Hanumana comes to know that this lady is not Mata Sita. That Lady was Mandodari who was also devoted to her husband Ravana and humble like Mata Sita was devoted to Lord Rama.
11 ) Mandodari had 3 sons with Ravana who were Meghnad, Akshaya kumara and Atikaya.
12 ) She tells Ravana to respect Sita and lawfully leave her to her Lord Rama but he doesn't listen to Mandodari and also his brother Vibheeshana who tries to tell him how divine is Lord Rama and Mata Sita.
13 ) After Ravana is slayed via Lord Rama Mandodari laments on his fate with the other wives of her husband Ravana.
14 ) She wishes to end her life but Lord Rama stops her and asks her to marry Vibheeshana and rule Lanka because she was the Queen and she couldn't end her life like this because she had duties towards the people of Lanka. That's why she marries Vibheeshana.
15 ) Mandodari is one of the Panchakanyas the five women whose name once said dispels sins.