Bitcoin is a path breaking innovation and I am sure that Satoshi is not a single human. A group is definitely behind the bitcoin's development. Otherwise, it wouldn't have been possible to make bitcoin so immensely popular. There was a structured workforce for all the hard work done behind bitcoin.
I don't think that's necessarily true. Whether Satoshi was an individual or a group has no bearing on its level of popularity. If you read through Satoshi's early posts (on the mailing lists and here on bitcointalk), his writing style was very recognizable. If it was a group effort, they were
very careful only to have one designated "face" to the world.
Satoshi wasn't the best coder (there were some big mistakes made early on), and he himself said that the work of Bitcoin was mostly about the
design and not the code. From that perspective, it makes sense to me that he was the initial architect, but not the most capable steward to deliver Bitcoin to the world. Thank goodness for Core.
If it's anyone on that list, I think it's Nick Szabo. Very cryptography and design-oriented, and less code-oriented.