Robert m. Proto-Germanic *hrōþiz 'fame' + Proto-Germanic *berhtaz 'bright'.
The name of two 8th C German saints, a 10th C king of West Francia, a 10th-11th C king of the Franks, an 11th C French saint, a 12th C French saint, a 12th C English saint, a 14th C king of Germany, a 14th C king of Naples, three 14th C kings of the Scots, and a 15th C king of Germany.
The Norman name arrived in England with the Conquest, but the Old English cognate was found rarely, earlier.
The English diminutives Dob, Dobe, Hob, Hobbe, Rob, Roben, Robin, and Robyn are witnessed in 1379 in the relational bynames Dobsoñ (WRYPT1 p. 29), Dobesoñ (WRYPT1 p. 295), Hobsoñ (WRYPT1 p. 22), Hobbesoñ (WRYPT1 p. 10), Robsone (WRYPT1 p. 13), Robensoñ (WRYPT1 p. 43), Robinwyf' (WRYPT1 p. 9), and Robynsone (WRYPT1 p. 13).