Thanks very much pond50. I did look back a few pages before i posted the question just to check and nothing came upon the check list. I have found the other entry now but am still confused about the explanation. I do like to get the answer to fit the clue.
Flipper, someone who flips from one thing to another, hence "person becoming". (OED has flipper "an unrelaible person", though this usage is flagged as rare in my edition. I agree it's not a brilliant clue. Perhaps "Person changing a famous dolphin" would have been better?)