The two supreme sharavakas were Buddha Shakyamuni's two foremost disciples:

They were both born on the same day near Rajagriha, the capital of Magadha, in families with close ties and grew up together. It is through Ashvajit that they first heard of Buddha Shakyamuni's teachings. They both passed away into nirvana one year before the Buddha.

Further Reading

Buddha Shakyamuni's Disciples Historical Masters Enumerations 02-Two