Historical clue formulations

• Dr. Seuss' environmentalist — 2026-09-24
• Titular Dr. Seuss character — 2026-03-21
• Literary character who cries "You're glumping the pond where the Humming-Fish hummed!" — 2024-03-13
• Eco-conscious Dr. Seuss character — 2018-09-17
• Title Seuss creature — 2017-08-20
• See 9-Down — 2017-04-09
• Once-ler's opponent, in children's literature — 2017-02-24
• Seussian environmentalist — 2016-12-01
• Title Seuss character, with "the" — 2016-06-15
• Dr. Seuss environmentalist — 2015-11-01
• Hit 2012 animated film, with "The" — 2013-07-18
• Seuss character who "speaks for the trees" — 2011-07-21
• Environmentalist in a Dr. Seuss story — 2010-07-19
• Truffula Tree defender, with "the" — 2009-06-12
• Dr. Seuss book, with "The" — 2008-04-25
• 44-Across character, with "the" — 2007-11-22
• Seuss title creature — 2001-05-09
• Seuss creature — 1997-04-12