I'm looking for a possibly derogatory noun that describes a person who changed their view from what they believed before. It could also be used to describe a person who expresses different views to different people when asked about the same issue.
For instance: Ben always says that landing on the moon was real, but when talking to Melissa, he suddenly says that it was faked. He's such a ______.
I've tried googling this word, but "fickle" is the only one I can find. "Double standards" does describe the view, but I vividly remember there being a noun to describe a person like this.
I saw a Tumblr post related to this a while ago as well. It said something along the lines of "Changing your mind doesn't make you a ______, it means you've grown." I'm fairly certain the word ended in -ist as well, but those are all the details I can recall.