Short answers, pulled from the story.
Alamgir II, born Mirza Aziz-ud-Din on the 6th of June 1699, was the fifteenth Mughal emperor, reigning from 1754 to 1759. He was the son of Jahandar Shah and spent forty years as a prisoner before ascending the throne at the age of fifty-five.
Alamgir II was imprisoned in 1714 by Asaf Jah I under the emperor Farrukhsiyar, after his father Jahandar Shah was defeated in the Mughal war of succession. He remained in captivity from 1714 until 1754.
Alamgir II was assassinated in November 1759 by agents of his own vizier, Imad-ul-Mulk. Imad-ul-Mulk feared that the emperor would use his son Prince Ali Gauhar, who had escaped Delhi, to overthrow the vizier's regime. The assassination took place at Kotla Fateh Shah, where the emperor was lured under the pretense of meeting a holy man.
Alamgir II and Ahmad Shah Durrani formed a formal alliance cemented by two dynastic marriages in 1757. Alamgir II's daughter Zuhra Begum married Timur Shah Durrani, and Ahmad Shah Durrani himself married Hadrat Begum, daughter of the former emperor Muhammad Shah.
The Marathas, supported by Alamgir II's vizier Imad-ul-Mulk, besieged Delhi in July 1757, cut off food supplies, and looted the city after the emperor fled to Bharatpur State. The Peshwa also publicly stated his intention to place Vishwasrao on the Mughal throne in the emperor's stead.
Prince Ali Gauhar escaped from Delhi before his father's assassination in 1759. He later became the Mughal emperor Shah Alam II and, according to the source, placed Delhi under his nominal authority after Najib-ud-Daula and Ahmad Shah Abdali recaptured it from the Marathas.