Theodemer (also Theudomer) was a Frankish king in the early 5th century. He was the son of Richomeres and his wife Ascyla. He is mentioned by Gregory of Tours, who wrote in the 6th century.
He is also apparently mentioned in the Chronicle of Fredegar, written in the 7th century, which says that the father of the Frankish king Chlodio was named Theodemer.
If his father was the Roman commander called Richomeres, then Theodemer may have been a cousin of Arbogastes.