Chlothar I (c. 497 – 29 November 561) was a king of the Franks of the Merovingian dynasty and one of the four sons of Clovis I.

Chlothar's father, Clovis I, divided the kingdom between his four sons. In 511, Clothar I inherited two large territories on the Western coast of Francia, separated by the lands of his brother Childebert I's Kingdom of Paris. Chlothar spent most of his life in a campaign to expand his territories at the expense of his relatives and neighbouring realms in all directions.

His brothers avoided outright war by cooperating with Chlothar's attacks on neighbouring lands in concert or by invading lands when their rulers died. The spoils were shared between the participating brothers. By the end of his life, Chlothar had managed to reunite Francia by surviving his brothers and seizing their territories after they died. But upon his own death, the Kingdom of the Franks was once again divided between his own four surviving sons. A fifth son had rebelled and was killed, along with his family.

Chlothar's father, Clovis I, had converted to Nicene Christianity, but Chlothar, like other Merovingians, did not consider that the Christian doctrine of monogamy should be expected of royalty: he had five wives, more from political expediency, for the purpose of forming alliances, than for personal motives. Although at the instigation of his queens he gave money for several new ecclesiastical edifices, he was a less than enthusiastic Christian and succeeded in introducing taxes on ecclesiastical property.