Tumbler is the name shared by two characters from the Marvel Universe.
Tumbler (John Robert Keane)
The Tumbler, alias John Robert Keane, trained with the acrobats, strongmen and jugglers at a circus to master their skills after being rejected by a gang. His training complete, he decided to take on Captain America, planning to make his name by defeating the hero. Although he believed he succeeded in defeating the hero (it was actually the Adaptoid), he was soon trounced by the real Captain America.
The Tumbler was later slain in an attempt to frame the Captain for his murder.