Trpimir I (Croatian pronunciation: [tpimir pi], Latin: Trepimerus/Trepimero) was a duke (Croatian: knez) in Croatia from around 845 until his death in 864. He is considered the founder of the Trpimirovi dynasty that ruled in Croatia, with interruptions, from around 845 until 1091. Although he was formally vassal of the Frankish Emperor Lothair I, Trpimir used Frankish-Byzantine conflicts to rule on his own.

Knyaz or knez (князь) is a historical Slavic title, used both as a royal and noble title in different times of history and different ancient Slavic lands. It is usually translated into English as prince, duke or count, depending on specific historical context and the potentially known Latin equivalents of the title for each bearer of the name. In Latin sources the title is usually translated as comes or princeps, but the word was originally derived from the common Germanic *kuningaz (king).The female form transliterated from Bulgarian and Russian is knyaginya (княгиня), kneginja in Slovene and Serbo-Croatian (Serbian Cyrillic: кнегиња), kniahinia (княгіня) in Belarusian and kniazioŭnia (князёўна) is the daughter of the prince, kniahynia (княгиня) in Ukrainian. In Russian, the daughter of a knyaz is knyazhna (княжна). In Russian, the son of a knyaz is knyazhich (княжич in its old form).The title is pronounced and written similarly in different European languages. In Serbo-Croatian and some West Slavic languages, the word has later come to denote "lord", and in Czech, Polish and Slovak also came to mean "priest" (kněz, ksiądz, kňaz) as well as "duke" (knez, kníže, książę, knieža). In Sorbian it means simply "Mister" (from "Master". Compare French monsieur from mon sieur "my lord"). Today the term knez is still used as the most common translation of "prince" in Slovenian, Bosnian, Croatian and Serbian literature. Knez is also found as a surname in former Yugoslavia.