Short answers, pulled from the story.
Harsha, full name Harshavardhana, was the emperor of Kannauj from April 606 until his death in 647. He was the king of Thanesar, the younger brother of Rajyavardhana, and the son of Prabhakaravardhana, and he ruled a vast realm across northern India.
Harsha ascended the throne at the age of 16 after his brother Rajyavardhana was treacherously murdered by Shashanka, the King of Gauda. In April 606, representatives of small republics from Punjab to central India crowned him emperor at an assembly and gave him the title Maharajadhiraja.
Harsha was defeated because he tried to expand his empire into the southern peninsula of India, and Pulakeshin II of the Chalukya dynasty repelled the invasion on the banks of the Narmada in the winter of 618-619. The two then signed a treaty making the Narmada River the border between their empires.
The Chinese traveller Xuanzang visited Harsha's court and wrote a very favourable account of him, calling him Shiladitya and praising his justice and generosity. Xuanzang described Harsha as a devout Buddhist who banned animal slaughter, built monasteries and stupas, and held a great assembly called Moksha every five years.
Harsha is widely believed to be the author of three Sanskrit plays: Ratnavali, Nagananda, and Priyadarsika. Some hold that his court poet Dhāvaka wrote them as a paid commission, while Wendy Doniger is persuaded that Harsha wrote the plays himself.
After Harsha died, the Tang envoy Wang Xuance arrived in 648 and was attacked by the new king Aluonashun. Wang escaped to Tibet, raised a force of over 7,000 Nepalese and 1,200 Tibetan troops, and in 649 took 2,000 prisoners from Magadha at the Battle of Chabuheluo, capturing the Indian pretender.