Short answers, pulled from the story.
Maitreya is a bodhisattva prophesied to become the next Buddha in all schools of Buddhism. Regarded as the direct successor of Gautama Buddha, he is the fifth and final Buddha of the current cosmic era. He currently resides in Tushita heaven and is expected to descend to Earth 5,670,000,000 years from now.
Maitreya derives from the Sanskrit word maitrī, meaning friendliness or loving-kindness, which itself comes from the noun mitra meaning friend. In Tibetan Buddhism he is called Pakpa Jampa, meaning the Noble Loving One or Lord of Love. He is also referred to as Ajita, meaning Invincible, in texts such as the Lotus Sutra and the Amitabha Sutra.
According to Buddhist tradition, Maitreya currently resides in Tushita heaven, dwelling in a palace at the center of that celestial realm. Both Theravada and Mahayana traditions share this belief. Mahayana masters including Dao'an, Xuanzang, and Yijing expressed devotion aimed at being reborn there to receive teachings from him.
The Five Dharmas of Maitreya are scriptures traditionally said to have been transmitted to the 4th century Indian master Asanga after he encountered Maitreya in a vision. The Tibetan tradition lists them as the Mahāyānasūtrālamkārakārikā, Dharmadharmatāvibhāga, Madhyāntavibhāgakārikā, Abhisamayalankara, and the Ratnagotravibhaga. The Chinese tradition names a partially different set, including the Yogācārabhūmi.
The Buddhist prophecy of Maitreya's coming during an age of moral decline gave religious legitimacy to groups opposing established rulers. During the Sui Dynasty alone, three separate leaders claimed to be Maitreya and launched insurrections, in 610 and 613 CE. Later movements including the White Lotus Society and the Red Turban Rebellion (approximately 1351-1368) also invoked Maitreya to challenge dynastic authority.
Maitreya is typically shown standing or sitting on a throne, dressed as a northern Indian nobleman with flowing robes, jewels, and a full head of hair. In Gandharan style he has a distinctive long hair loop folded at the top of the head. He frequently carries a water vessel called a kamaṇḍalu, a symbol associated with immortality, wisdom, and abundance that he shares with depictions of the deity Brahma.