The next Buddha will be Metteyya (Maitreya)

G.P. Malalasekera (Pali Proper Names); Amber Larson and Dhr. Seven (eds.), Wisdom Quarterly

Maitreya, the spiritual friend, is The Future Buddha, a kind of Buddhist messiah.

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The future supremely enlightened teaching buddha

The next buddha will be the fifth of this aeon or kalpa (Bu.xxvii.21).

According to the "Wheel-Turning Monarch Discourse" (Cakkavatti Sīhanāda Sutta, DN 26), he will be reborn far in the future when beings  in the human plane (which includes many worlds in many world systems far from earth, as Buddhist cosmology is better understood not as separate continents -- dipas or "islands" -- but  as separate planets) again live to an age of 80,000 years.

• DN 26 is a sutra preached in Mātulā that tells the story of humanity's decline from the most recent Golden Age with a prophecy of its eventual return (because time is cyclical).
• The name Metteyya comes from metta (Sanskrit Maitreya from maitri). It means "friend," because buddhas are the best friend (kalyana-mitta) anyone could possibly have.

He will be reborn in the city of Ketumatī (present-day Benares, a.k.a. Varanasi), whose king will be the World Monarch (cakka-vattī) Sankha.

King Sankha will live in the fairy palace where King Mahāpanadā once dwelled, but later he will give the palace away and will himself become a follower of Metteyya (Maitreya) Buddha (D.iii.75ff).

The Anāgatavamsa (J.P.T.S.1886, pp.42, 46ff., 52; DhSA.415) gives the names of his parents and further particulars.

Himalayan Maitreya as a Central Asian king

The Buddha Metteyya will be reborn in a very eminent Brahmin family, and his personal name will be Ajita. Metteyya is evidently the name of his clan (gotta).

For 8,000 years he will live the household life in four palaces: Sirivaddha, Vaddhamāna, Siddhattha, and Candaka.

His chief wife will be Candamukhī and his son will be Brahmavaddhana. Having seen the four signs while on his way to the park, he will become dissatisfied with household life and will spend one week practicing severe austerities.

Then he will leave home, traveling in his palace and accompanied by a fourfold army, at the head of which will be 84,000 Brahmins and 84,000 khattiya (warrior princess) maidens.

Among his followers will be Isidatta and Pūrana, two brothers, Jātimitta, Vijaya, Suddhika and Suddhanā, Sangha and Sanghā, Saddhara, Sudatta, Yasavatī and Visākhā, each with a retinue of 84,000 companions.

Together they will leave the household life and arrive on the same day at the enlightenment (bodhi) tree. After the enlightenment Metteya, when he becomes a supremely awakened buddha, he will teach in Nāgavana.

King Sankha will later ordain himself under him. Metteyya's father will be Subrahmā, chaplain (Brahmin minister) to King Sankha, and his mother will be Brahmavatī.

His chief male disciples will be Asoka and Brahmadeva among his monks, and Padumā and Sumanā will be his chief female disciples among his nuns.

Sīha will become his personal attendant, and his chief patrons will be Sumana, Sangha, Yasavatī, and Sanghā.

His enlightenment tree will be the nāga tree. After the Buddha's passing into final nirvana, his Dharma or Teaching will persist for 180,000 years.

According to the Mahāvamsa (Mhv.xxxii.81f.; see Mil.159), Kākavannatissa and Vihāramahādevī, father and mother of Dutthagāmani, will be Metteyya's parents. Dutthagāmani himself will be his chief disciple, and Saddhātissa his second disciple, while Prince Sāli will be his son.

Maitreya in Tusita (palm-leaf manuscript)

At the present time the Future Buddha is living in the Tusita deva-world (Mhv.xxxii.73), as is the case of all buddhas-to-be awaiting rebirth in the human plane.

There is a tradition that Nātha is the name of the Future Buddha in the deva world.

The worship of the Bodhisatta Metteyya seems to have been popular in ancient Ceylon, and Dhātusena adorned an image of him with all the equipment of a king and ordained a guard for it within the radius of seven yojanas (Cv.xxxviii.68).

King Dappula I. made a statue in honor of the Future Buddha 15 cubits high (Cv.xlv.62). It is believed that Metteyya spends his time in the deva-world, teaching the Dharma to the assembled devas and, in emulation of his example, King Kassapa V. used to recite the Abhidhamma in the assemblies of the monks (Cv.lii.47).

King Parakkamabāhu I. had three statues built in honor of Metteyya (Cv.lxxix.75), while Kittisirirājasīha erected one in the monastery Rajata Vihāra and another in the cave above it (Cv.c.248,259).

It is the wish of many Buddhists that they meet Metteyya Buddha, listen to his Dharma, and thereby attain enlightenment and nirvana under him. (See, e.g., J.vi.594; MT. 687; DhSA.430). Source