When I started my travels in Yucatán in 1975, only a handful of Maya glyphs had been deciphered. In fact, one prominent archeologist—J. Eric S. Thompson—was of the opinion that such glyphs as existed were primarily calendrical. Earlier archeologists had deciphered the vigesimal (base 20) numbering system of the Maya as well as the day glyphs for the two calendar systems. But the notion that the glyphs provided names and descriptions of events was considered as far-fetched. It was Sir J. Eric S. Thompson who felt that ancient Maya was anti-phonetic.
It took two Russians to show that, yes, the Maya did have a history, and that the history was described on commemorative stelae at the various ruins.
First came Tatiana Proskouriakoff (1909-1985), born in Tomsk, who spent much of her professional life with Harvard University and its Peabody Museum. It was she who made a key discovery. According to Wikipedia:
Her greatest contribution was considered the breakthrough for Maya hieroglyphic decipherment in the late 1950s and early 1960s. While researching the chronology of changing styles of Maya sculpture, she discovered that the dates shown on the monumental stelae were actually historical, the birth, accession, and death dates for Maya rulers. Analyzing the pattern of dates and hieroglyphs, she was able to demonstrate a sequence of seven rulers who ruled over a span of two hundred years. Knowing the context of the inscriptions, Maya epigraphers were then able to decipher the hieroglyphs.
The next key person was one of her countrymen who had never even seen a Maya ruin first hand:
It was only after Thompson died in 1975 that the work of Yuri Knorozov came to the fore. During the height of the Cold War, he wrote a paper entitled “The Writing of the Maya Indians” (1963), followed by his own translations of many of the glyphs. His work opened the floodgates. New scholarly works on the Maya archeological sites come with dates, names, and even history.
If you are interested in the subject, I recommend you read Michael D. Coe’s Breaking the Maya Code, Third Edition (2012). The book is dedicated to Knorozov and his work.