Possible Clues:

• Hit 2012 animated film, with 'The'
• Seuss character
• Seuss's nature spokesman
• Character voiced by Danny DeVito, with "The"
• Ecological character voiced by Danny DeVito, with 'The'
• 'Mossy, bossy' Dr. Seuss character
• Ecological Seuss character, with 'The'
• Dr. Seuss' environmentalist
• Seuss's environmental advocate
• Seuss book with environmental undertones, with 'The'