When Moses journeyed to the summit of Mount Sinai in order to receive the Ten Commandments, he left the Israelites for forty days and forty nights. The Israelites, fearing that Moses would not return, asked Aaron to make gods for them. Aaron complied and gathered up the Israelites' golden earrings. He melted them and constructed the golden calf.
The people said it was their god which led them out of Egypt.