According to Hindu mythology, the roots of Diwali are traced to both Satyuga and Tretayuga. In Tretayuga, it's associated with Lord Ram's return to Ayodhya. In Satyuga, which precedes Tretayuga, it's linked to Goddess Laxmi's appearance after 'Samudra Manthan'. It's also believed she adopted Lord Ganesh and said only those who worship both of them together would get prosperity.