Peter Dajnko (23 April 1787 – 22 February 1873) was a Slovene priest, author, and linguist, known primarily as the inventor of an innovative proposal for the writing system for Slovene: the Dajnko alphabet (Slovene: dajnčica).
He was born in the village of Črešnjevci near the town of Gornja Radgona, in what was then the Duchy of Styria in the Habsburg Monarchy. After finishing high school in Maribor, he studied theology and philosophy at the University of Graz, where he graduated in 1814.
In 1824 he wrote a book in German called Lehrbuch der windischen Sprache (Textbook of the Slovene Language). In it, he proposed the adoption of a new alphabet for Slovene, which was to replace the traditional Bohorič alphabet, used since the late 16th century. According to Dajnko, the old script had shown clear deficiencies, since it did not fit well with the phonetic structure of Slovene. Dajnko's proposal, which included several characters not found in the Latin script, created a long-lasting controversy, which became known as the "War of Letters" (Slovene: črkarska pravda). Among Dajnko's fiercest opponents were the philologist Matija Čop and the poet France Prešeren, while he did enjoy some initial support from the linguist Jernej Kopitar. In 1825, Franc Serafin Metelko came up with a similar proposal, further complicating the issue.
After 1839 his proposal became obsolete with the adoption of a slightly modified version of Gaj's Latin alphabet as the new Slovenian script. Dajnko nevertheless continued to use his own alphabet in all his later Slovene books.
Dajnko was also a professional beekeeper and introduced several innovations in apiculture, following the example of his fellow countryman Anton Janša.
He died in the town of Velika Nedelja in his native Lower Styria.