Gaj started publishing very early; his 36-page booklet on stately manors in his native district, written in his native German, appeared already in 1826 as Die Schlösser bei Krapina. In Buda in 1830 Gaj's Latin alphabet was published , which was the first common Croatian orthography book. The book was printed bilingually, in Croatian and German. The Croatians used the Latin alphabet, but some of the specific sounds were not uniformly represented. Gaj followed the example of Pavao Ritter Vitezović and the Czech orthography, using one letter of the Latin script for each sound inthe language. He used diacritics and the digraphs lj and nj. The book helped Gaj achieve nationwide fame. In 1834 he succeeded where fifteen years before Đuro Matija Šporer had failed, i.e. obtaining an agreement from the royal government of the Habsburg Monarchy to publish a Croatian daily newspaper. He was known as an intellectual leader thereafter. On 6 January 1835, Novine Horvatske appeared, and on 10 January the literary supplement Danicza horvatzka, slavonzka y dalmatinzka. The "Novine Horvatske" were printed in Kajkavian dialect until the end of that year, while "Danica" was printed in Shtokavian dialect along with Kajkavian. In early 1836 the publications' names were changed to Ilirske narodne novine and Danica ilirska respectively. This was because historians at the time hypothesised Illyrians had been Slavic and were the direct forefathers of the present-day South Slavs. In addition to his intellectual work, Gaj was also a poet. His most popular poem was "Još Hrvatska ni propala", which was written in 1833.
The Latin alphabet used in the Serbo-Croatian language is credited to Gaj's Kratka osnova Hrvatskog pravopisa. The Cyrillic counterpart is called vukovica, after contemporary linguist Vuk Karadžić. The Slovenian alphabet, introduced in the mid-1840s, is also a variation of Gaj's Latin alphabet, from which it differs by the lack of the letters ć and đ.
Personal
He married 26-year-old Paulina Krizmanić, niece of an abbott, in 1842 at Marija Bistrica. They had five children: daughter Ljuboslava, and sons Velimir, Svetoslav, Milivoje, and Bogdan.
Legacy
In 2008, a total of 211 streets in Croatia were named after Ljudevit Gaj, making him the fourth most common person eponym of streets in the country.