Some personal thoughts here...
I do tend to agree with Fudugazi that the list is oriented to tarot history; knowing that jmd and the Association for Tarot Studies tend to be historically oriented, I'm not surprised.
I assume jmd started this thread to seek input for additional nominations of, and personal opinions of, important contributers who, through their life's work, have dramatically improved our understanding/appreciation of Tarot.
I commend jmd and the ATS for opening up the discussion and seeking this feedback, but ultimately, this is not an Aeclectic award. This is an opportunity to communicate with the ATS members who are continuing a tradition of recognizing outstanding contributions to Tarot.
There are many names on the list that I feel have significantly contributed to Tarot:
Ronald Decker
Thierry Depaulis
Michael Dummett
The contributions of these three authors has changed our understanding of the history of tarot. Their books together, and solitary contributions, have set the standard for our understanding of Tarot History and Iconography.
Jean-Claude Flornoy
For his contributions to the exploration of Tarot History, but most specifically for his artistic craftsmanship recreating decks, using modern and antique methods, from the 1600s and 1700s.
Mary Greer
Rachel Pollack
For their books and workshops which introduce so many people to tarot, and further educate all levels of study. As I mentioned earlier, I think Mary's contributions to documenting the history of divination with Tarot is also very important.
Osvaldo Menegazzi
For his contributions with the Il Meneghello series of decks. This series of reproductions set the highest standard of quality.
Robert O'Neill
His book "Tarot Symbolism", and contributions to Tarot.com's library, are foundational for the study of Tarot symbolism.
Andrea Vitali
For his landmark work on the Bologna, and his contributions to catalogs and exhibitions for tarot.
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But even with this list, there are several names that I feel have contributed so universally, that I could narrow it down to 3 or 4.
When adding new names to the list, I have to compare them to the names already present. If anything, I'm having a hard time narrowing it down once I reach that top 3 or 4.
For me, that short list would include Michael Dummett, Mary Greer, Robert O'Neill, and Rachel Pollack.