Authari (c. 540 – 5 September 590, Pavia) was king of the Lombards from 584 to his death. After his father, Cleph, died in 574, the Lombardic nobility refused to appoint a successor, resulting in ten years interregnum known as the Rule of the Dukes.
In 574 and 575 the Lombards made the blunder of invading Provence, then part of the kingdom of Burgundy of the Merovingian Guntram. Guntram, allied with his nephew, the king of Austrasia, Childebert II, invaded Lombardy. The Austrasian army descended the valley of the Adige and took Trent. The Byzantine emperor, Tiberius II, began to negotiate an alliance with the Franks and the Lombards, fearful of a pincer movement, elected another king.
In 584, they elected Duke Authari and ceded him not only the capital of Pavia, but half of their ducal domains as a demesne. He spent his entire reign in wars with Franks, Greeks, and rebels. His first major test was the quashing of the rebel duke Droctulf of Brescello, who had allied with the Romans and was ruling the Po valley. Having expelled him, he spent most of the rest of his six years on the throne fighting the exarch of Ravenna, Smaragdus, or the Merovingian kings.
Guntram and Childebert were still not satisfied with their successes in Italy and they many times threatened invasion, following through on their threats twice. The memory of Theudebert I of Austrasia's campaigns in Italy, the urging of Childebert's warlike mother Brunhilda and the Byzantine emperor and exarch, as well as the wrongs done Guntram in the past undoubtedly fueled their quarrelsomeness. In 588, Authari defeated them handily, but in 590, the uncle and nephew led to armies across the Alps, respecitvely over Mont Cenis and the Brenner to Milan and Verona. Though Authari shut himself up in Pavia, the Franks accomplished little as the exarch's army did not meet them and the could not even join up with each other. Pestilence turned them around and they left the Lombards much chastened, but hardly defeated.
Authari, when not controlled by foreign armies, expanded the Lombard dominion at the expense of Byzantium. He took the fortress of Comacchio and cut of communication between Padua and Ravenna. Faroald, duke of Spoleto, captured the Ravennan seaport of Classis and utterly devastated it. Authari swept through the peninsula all the way to Reggio, vowing to take Calabria — a vow never to be kept by any Lombard.
On 15 May 589, he married Theodelinda, daughter of the Bavarian duke Garibald I. A Catholic, she had great influence among the Lombards for her virtue. When Authari died in Pavia in 590, possibly by poison, he was succeeded as king by Agilulf, duke of Turin, on the advice, sought by the dukes, of Theodelinda, who married the new king.