ultimate: adj. - the best, most, or greatest of its kind (Cambridge Dictionary).
This is an attempt to create an approximation of an ultimate list. It combines 6 challenges with ultimate in their title into one. Each original challenge had at least 1000 users and did not emphasise one genre. Two of my own challenges are included. Hopefully all duplicates have been eliminated (a series title and its individual books can coexist).
The challenges used were:
Ultimate Book List (Desiree Amber Moore)
Ellie's Ultimate Book Bucket List (Ellie-Jean Royden)
The Ultimate Reading List (Ellen Nicole Allen)
The ULTIMATE ULTIMATE ULTIMATE Reading List (Purplepopcornkr81)
Ultimate List: Top 100 Kindle Books of All Time (Markd9528)
Updated - The Ultimate List - 100 Books to Read Before You Die (Markd9528)
Thanks to the original list publishers. 1822.