In his previous birth, Arjuna was a saint Nara. His lifelong companion then was saint Narayana, an avatar of Lord Vishnu.
The word Arjuna in Sanskrit means silver, clear or white. In the Mahabharata period, he was also called as Vijaya, Dhananjaya, Parantapa, Shvethavahana, Savyasachin, Partha...