Did Champollion really crack hieroglyphs alone, or did he borrow Thomas Young's key?

Champollion built the working method himself, but he did not start from nothing: the British polymath Thomas Young had made the first phonetic steps, and some still argue that Champollion should have acknowledged them.

Young worked from the Rosetta Stone beginning in 1813, using an alphabet of demotic letters built by Johan David Åkerblad (14 of its 29 letters turned out to be wrong). He found the phonetic signs for the name Ptolemaios in the hieroglyphic text and noted as many as 80 similarities between the hieroglyphic and demotic texts, deducing correctly that demotic was only partly phonetic. But he worked without identifying the language of the text. By comparing how often words appeared in the Greek and Egyptian texts, he could point out which glyphs spelt "king", but could not read the word.

Champollion believed from a young age that Coptic was the last stage of ancient Egyptian and the key to the hieroglyphs. He reasoned that if the script were purely ideographic, the hieroglyphic text would need as many signs as the Greek had words, but it had fewer, so the script mixed ideographic and phonetic signs. Using the names Ptolemy and Cleopatra, he determined the phonetic value of 12 signs and soon read dozens of other names.

The bitter part is the credit. Young was offended that Champollion's 1822 letter mentioned him only twice, and one of them was harsh. Champollion never admitted any debt to Young's work. His decipherment is now universally accepted and has been the basis for all further developments in the field.