Lord Krishna is the Supreme Personality of Godhead, as described by the Vedas. The Vedas are the eternal truths of life originating in India that have been passed down from time immemorial originally through oral reception, and more recently through written scripture in the Sanskrit language. Though there are many different religions in the world each having their own name for God, God is still one. There isn’t one God for Hindus and another for Christians and Jews.
Even in the Vedic literatures, God has many names and many different incarnations and expansions. Lord Krishna is the original of all other expansions. In Sanskrit, the word Krishna means “all-attractive.” Krishna is the most beautiful, powerful, famous, beautiful, wise and renounced. Since He possesses all these opulences at the same time and in full, He is defined as the Supreme Personality of Godhead.
Lord Krishna personally appeared on this planet some five thousand years ago in Mathura, India. The reasons behind his advent were many, but they were primarily to kill the demon Kamsa and give protection and salvation to His devotees. Krishna was born as the eighth son of his father and mother, Vasudeva and Devaki. At the time of his birth, Krishna’s parents were prisoners of Devaki’s brother King Kamsa. A prophecy had warned Kamsa that he would one day be killed by Devaki’s eighth son. Thus Kamsa had killed every one of Devaki’s first seven children and was planning on doing the same to Lord Krishna. In order to protect his newborn son, Vasudeva transported Krishna to Vrindavan.
In Vrindavan, Lord Krishna was raised by his foster parents Nanda Maharaj and Yashoda. He enacted many wonderful pastimes in his childhood. Krishna has many different names, such as Govinda, Gopala, Giridhari, Damodara to name a few. These names are all based on His different pastimes and activities. The Lord grew up as a cowherd and He brought joy to all who lived in Vrindavan. In pictures, Krishna is usually seen standing with his eternal consort, Shrimati Radharani. 
She is Lord Krishna’s pleasure potency and His most beloved devotee. She is always thinking of Krishna, and therefore we worship her along with Krishna.
During Lord Krishna’s time, there was a great war that took place between the Pandava and Kaurava dynasties on the battlefield of Kurukshetra in India. Arjuna was one of the leading warriors for the Pandavas. Since Arjuna was Lord Krishna’s good friend and cousin, the Lord served as his charioteer during the war. Prior to the war’s commencement, Arjuna felt hesitant to fight, and so Lord Krishna stopped and gave him a discourse on the meaning of life. Their discussion has been chronicled in the famous book, Bhagavad-Gita.
The Gita is a highly philosophical book, but its essential instruction is that the true purpose of life is to surrender under Lord Krishna, or God, through the practice of bhakti yoga, or devotional service. Devotional service involves the nine processes of hearing, chanting, remember, worshipping, serving the lotus feet of the Lord, offering prayers, carrying out the orders of the Lord, making friends with Him, and surrendering everything to Him. Engaging in any or all of these processes will surely make our lives perfect.
Vedic literature such as the Bhagavata Purana (Shrimad-Bhagavatam), Hari-Vamsha, Mahabharata, Bramhavaivarta Purana, and many others describe Lord Krishna’s pastimes in much greater detail. Immersing oneself in any of these literatures with faith and devotion to Krishna will guarantee one of bliss and happiness in this life and the next. Krishna’s Mercy is dedicated to serving the lotus feet of Lord Shri Krishna.