Shri Laxmi has a long and interesting history. The same is testified by the fact that the first hymn in her stuti - Shri Shukta was added to the Rig Veda. Rig Veda was composed in 1000 to 500 BC.
She is also very popular among Buddhist and Jains. It is believed that her worship predates the Vedic culture and had developed independently before being recorded in any form. Stories of Laxmi also appear in epics like Ramayana and Mahabharata that were composed in 300 BC and 300 AD.
As per Vishnu Puranas, Lord Vishnu is the celestial being and He is an ever powerful Lord. He created the universe and then gave life to Lord Shiva and Brahma. At the same time, he gave life to his consort Maa Laxmi.