The Supreme God. He has many names - God, the Supreme Being,  Parameshwar, Haru, Hari, Achyut, Vishnu, Vaasudev, Shiv etc.

Visnu Puraan, 6/3 says - "In this Bhagavat word, 'Bha' letter has two meanings - who has nourished everybody and who is the base of everything. 'Ga' means who gives the fruits of Karm and is Creator. So all riches (Aishwarya), Dharm, fame, Shree (auspiciousness), Gyaan (wisdom) and Vairaagya (detachment or dispassion) - these six are called 'Bhag'. In Him everybody lives, and He lives in everybody - that is the meaning of 'Vaan'. Thus this Bhagavaan word is the synonym of Vaasudev. Who knows about the creation and destruction of all beings, coming and going and Vidyaa and A-Vidyaa, only He is worthy to be called Bhagavaan."

In Agni Puraan, 32 Agni Dev says - "Hey Muni, There are two ways to attain Him - Gyaan and Karm. Gyaan is of two types - from Aagam and from Vivek. Gyaan of Shabd Brahm (books) is Gyaan through Aagam, and Gyaan of Par Brahm is Gyaan through Vivek. Brahm can be known in two ways - "Shabd Brahm" and "Par Brahm". Ved etc books are called "Shabd Brahm" or A-Par Brahm"; and Akshar, the form of Truth, is called "Par Brahm". This Par Brahm is the synonym of "Bhagavat".

"Bha" in Bhagavat has two meanings - one who nourishes and the supporter of all. Then "Ga" means leader (who assigns fruits to Karm), inspirer, and Creator. Prosperity, Dharm, fame, wealth, Gyaan and Vairaagya - all these 6 are "Bhag". All live in Vishnu. The same Vishnu has three forms - Brahmaa, Vishnu and Shiv, therefore "Bhag" is present only in Hari. For others it is used only secondarily. Who knows about the birth and death and coming and going of all Bhoot and Vidyaa and A-Vidyaa, the same is worthy to be called as Bhagavaan. Leaving all bad qualities, total Gyaan, Power, the ultimate prosperity, etc are synonyms of "Bhagavat".

As Ghee is always in the milk, fire is always in the wood, oil is always in sesame seeds, a plant is hidden in seed, in the same way Bhagavaan Vishnu also lives everywhere but we cannot see Him.
As milk has to be churned to take the Ghee out; or wood has to be rubbed together to ignite the fire, or seeds have to be ground to extract oil, and seed has to be sown in the ground to grow a plant, in the same way one has to meditate upon Vishnu to see Him.

Bhagavaan
Bhagavaan word is made up five letters and these five letters represent our 5 elements of nature, how? -

Bha - Bhoomi (Prthvi or Earth)
Ga  - Gagan (Aakaash or Ether)
Va  - Vaayu (Air)
A   -  Agni (Fire)
N  -  Neer (Jal or Water)

Thus you all are surrounded by HIM, so believe in HIM.