Double Dragon is a lot of things. It’s an 80’s style beat-um-up. It’s one of the earliest examples of two-player co-op. It’s the most successful game ever released by the Taito Corporation. It’s a reason sibling-on-sibling violence increased in 1987, due to the ability to beat your own co-player (this may be a joke; maybe).
What it is not is a single title. This is not in reference to the sequels, but the original game itself. Originally an arcade title, DD has since been translated onto no less than twenty consoles and operating systems. Almost every single one of them—by the very nature of the platform’s limitations—looked and played much differently. The NES even changes the main antagonist and gets rid of the co-op. How can this possibly be considered the same game as the arcade version?