noun / verb / adjective
rival
RY-vul/ˈraɪvl/
A competitor, or to compete with or match another in ability or achievement.
The chess player faces his rival across the board.

Etymology
The original image was someone belonging to the same brook. The competitive meaning seems to have developed from neighbors sharing a stream or living on opposite banks, hence pursuing the same resource or goal.
In context
Captain Absolute is literally his own rival. He's competing against the fake person he invented.
More examples
- Her newest painting rivals her best earlier work.
- The company bought out its largest rival.
- Several runners rivaled him for the national title.
Forms
rival · rivals · rivaled · rivaling
rivalry noun — ongoing competition
Similar words
- opponent
- Emphasizes direct opposition rather than a continuing competition.
- competitor
- More neutral; need not suggest a close or continuing contest.