When King Pelius sent Jason on a quest to find the Golden Fleece, he had much to do in preparation. He needed a crew, he needed supplies, and since the Golden Fleece was across the sea, in Colchis, he needed a boat.

Jason went to the best shipwright in Greece, Argus, and commissioned him to make a ship for his journey. In a fit of (possible) narcissism, Argus named the ship (kinda) after himself. It became known as the Argo, the greatest ship to ever sail in it's time, and the members of the Argo's crew were called the Argonauts. Jason's only specification for the Argo was that it needed spaces for 50 oars; however, Argus had more than just himself working on the Argo.

At Hera's request, the goddess Athena went to her father Zeus' sacred oak tree in Dodona and cut off a limb. She endowed this limb with powers of prophecy and speech and fitted it to the prow of the Argo. It gave Jason advice and counsel in times of dire need.

A telling of Jason's quest and the reasons behind it can be found here, so I won't waste your time, or E2 space, by telling it again. Suffice it to say, after embarking on several trials during their quest, the Argonauts finally got the Golden Fleece and returned to Greece, where Jason assumed his crown.

As an old man, Jason desired to see his old ship, the Argo, one last time; however, while visiting the Argo, the prophetic limb fell from the prow onto Jason's head, killing him.

After Jason's death, the gods wished to immortalize the Argo forever. They hung it in the sky, creating the constellation Argo.