I'll give a brief answer in two aspects of this question. 1) WHAT are important people to Buddhists. 2) WHO are important people to Buddhists. I suppose you had 2) in mind when writing the question but, what the hey?!

1) An important person to a Buddhist, in my view, is a person who does good things. Good for oneself as well as for others. Some Buddhists certainly wouldn't agree with this because of my use of the word "good". There are "good" reasons for this, but, I'm not going to get into it. Never mind.

2) Important people to Buddhists are first and foremost, Shakyamuni Buddha, or the guy we call the Buddha. There were Buddhas before him, and to some Buddhists, those Buddhas are important. Some important people since the Buddha are Buddhagosa, Sariputra, Bodhidharma, and The Sixth Patriarch (the latter two are important in Zen). The Dalai Lama is one of the few people alive today who are considered important in Buddhism. One could go on and on but ....

Answer: The most important people to Buddhism is Gods, human, animal, and everything that are alive in this world because his like gods he care about use he want people all around the world to do good stuff not bad stuff and not stuff that are stupid...:)

According to the Buddha, he and Vishnu are two different people. There are records of both talking to eaching other:

In the Maha-samya Sutta there was an occasion when the devas from almost all the planes came to see the Buddha when he was dwelling in the Great Wood together with 500 bhikkhus, all of them arahants. The Buddha introduced their names to the monks, Vishnu was one of those present. The Buddha mentioned him by the name Venhu.

The Venhu Sutta shows Vishnu as one of the young devas who came to visit and talked with the Buddha:

At Savatthi. Standing to one side, the young deva Venhu recited this verse in the presence of the Blessed One: " Happy indeed are those human beings attending on the Fortunate One. Applying themselves to Gotama's Teaching, who train in it with diligence."

The Blessed One said: "When the course of teaching is proclaimed by me, O Venhu," said the Blessed One, "Those meditators who train therein. Being diligent at the proper time. Will not come under Death's control."- The Connected Discourse of the Buddha" A Translation of the Samyutta Nikaya by Bhikkhu Bodhi ,page 432)

According to "Hinduism and Buddhism An Historical Sketch" (Vol. 2 page 746) , Sir Charles Elliot who was a British diplomat mentioned that this correlates with the Rig Veda text before Hinduism started. Both texts mentioned that Vishnu and Shiva are minor deities instead of the Lords of the Universe as popularly known by worshippers:

" Vishnu and Rudra (Shiva) are known even to the Rig Veda but as deities of no special eminence. It is only after the Vedic age that they became , each for his own worshippers, undisputed Lords of the Universe…..The Pali Pitakas frequently introduce popular deities , but give no prominence to Vishnu and Siva. They are apparently mentioned under the names of Venhu and Isana, but are not differentiated from a host of spirits now forgotten. ….The suttas of the Digha Nikaya in which these lists of deities occur were perhaps composed before 300 B.C. "- Sir Charles Elliot

Gautama Buddha in Hinduism is viewed as an Avatar of Vishnu.

In the Puranic text Bhagavata Purana, he is twenty fourth of twenty five avatars, prefiguring a forthcoming final incarnation.The text says that his teaching was to mislead "demons". I am not sure why that myth was created.

A number of Hindu traditions portray Buddha as the most recent of ten principal avatars, known as the "Dasavatara" (Ten Incarnations of God). The ten incarnations of Vishnu are: Matsya (fish), Koorma (tortoise), Varaha (boar), Narasimha (the man-lion), Vamana (the dwarf) Parasurama (the angry prince), Rama (the perfect human), Krishna (the divine statesman), Buddha and Kalki (the redeemer of righteousness in the kali Yuga, who is yet to appear).

The Buddhist Dasharatha Jataka (Jataka Atthakatha) represents Rama as a previous incarnation of the Buddha as a Bodhisattva and supreme Dharma King of great wisdom.However, the Jataka mentioned that Krishna was a past life of another person. It is Sariputra, the Buddha's chief disciple.

An influential Vaishnava poet Jayadeva Goswami (13th C AD), in the Dasavatara-stotra section of his Gita Govinda, includes the Buddha amongst the ten principal avatars of Vishnu and writes a prayer regarding him as follows:

O Keshava! O Lord of the universe! O Lord Hari, who have assumed the form of Buddha! All glories to you! O Buddha of compassionate heart, you decry the slaughtering of poor animals performed according to the rules of Vedic sacrifice.

This viewpoint of the Buddha as an avatar who primarily promoted non-violence (ahimsa) remains a popular belief amongst a number of modern Vaishnava organisations, including ISKCON(International Society for Krishna Consciousness).