Sir Robert Bruce Cotton (January 22 1570-May 6 1631) was an English politician, founder of the famous Cotton library.

He was of Huntingdonshire parentage and educated at Westminster School and Jesus College, Cambridge. He had become interested in antiquarian studies under William Camden, and began to amass a library. He entered Parliament as a member for Huntingdon in 1601. He helped devise the institution of the title baronet as a means for King James I of England to raise funds. Despite his early period of goodwill with James I, during which he was made a baronet, Cotton's politics became anti-royalist in nature and the authorities began to fear the uses of his library, which was confiscated in 1630 and returned only after his death to his heirs.

The Cottonian Library, the richest private collection of manuscripts ever amassed, was eventually donated to the nation by Cotton's grandson and now resides at the British Library.

The physical arrangement of Cotton's Library continues to be reflected in citations to manuscripts once in his possession. His library was housed in a 26 foot by 6 foot room filled with bookpresses , each with the bust of a figure from classical antiquity on top. Counterclockwise, these are catalogued as Julius (i.e., Julius Caesar), Augustus, Cleopatra, Faustina, Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Vespasian, Titus, and Domitian. (Domitian had only one shelf, perhaps because it was over the door.) Manuscripts are now designated by library, bookpress, and number: for example, the manuscript of Beowulf is designated Cotton Vitellius A.xv, and the manuscript of Pearl is Cotton Nero A.x.

Selected manuscripts

• Cotton Julius A.x Old English Martyrology
• Cotton Augustus II.106 Magna Carta: Exemplification of 1215
• Cotton Cleopatra A.ii Life of St Modwenna
• Cotton Faustina A.x Additional Glosses to the Glossary in Ælfric's Grammar
• Cotton Tiberius B.v Labour of the Months
• Cotton Caligula A.ii "A Pistil of Susan" (frag.)
• Cotton Claudius B.iv Genesis
• Cotton Nero A.x. Pearl
• Cotton Nero D.iv Lindisfarne Gospels
• Cotton Galba A.xviii Athelstan Psalter
• Cotton Otho C.i Ælfric's De creatore et creatura
• Cotton Vitellius A.xv Beowulf
• Cotton Vespasian D.xiv Ælfric's De duodecim abusivis
• Cotton Titus D.xxvi Ælfwine's Prayerbook
• Cotton Domitian A.viii Anglo-Saxon Chronicle (version E)