Robert E. O. Speedwagon is a core ally featured in Phantom Blood and is a minor ally in Battle Tendency. Speedwagon is a man who lived in darkness ever since he was born. Growing up on the dangerous Ogre Street, he stole things to live and met all kinds of horrible people in his life. It reached the point of him being able to tell a good person apart from a bad person just by their smell. He eventually became the leader of the thieves in Ogre Street and befriended a Kempo Master and Tattoo. During his youth, Speedwagon had traveled the world, experimenting with various exotic animals in Africa, strange Asian plants and Caribbean tornadoes.

Speedwagon first appears as an Ogre Street thug boss expecting easy pickings from Jonathan Joestar when he entered the street in search of the antidote to the poison that Dio Brando gave to his father. But finding himself outmatched, Speedwagon realized Jonathan spared his men and ordered the others to stand down, offering his services in leading Jonathan to Wang Chan. Fearing for Jonathan's safety, Speedwagon then accompanied him to the Joestar Mansion where he saw through Dio's attempt to lull Jonathan's guard with feigned remorse. When George died protecting his son from being stabbed by Dio, Speedwagon voiced his utmost respect to the Joestar family. Following Jonathan's battle against a newly vampirized Dio, Speedwagon takes Jonathan to the hospital where the youth was cared for by his childhood friend Erina Pendleton.

In the years following the death of Jonathan Joestar, Speedwagon had traveled to America, where he discovered oil and formed the powerful Speedwagon Foundation. It is also during this time that he became an uncle figure to Joseph Joestar, noting him as a dead-ringer of Jonathan despite their opposing personalities. At some point, Speedwagon was kidnapped on a hijacked plane and was going to be sold for ransom, if not for the efforts of Joseph.