Variant of Greg, short for Gregory, from Greek gregorios meaning 'watchful' or 'alert.'
Gregg is the double-g variant of Greg, itself the familiar short form of Gregory — a name with remarkably deep roots in Western intellectual and religious history. Gregory derives from the Greek Gregorios, formed from gregorein, 'to be awake, to be watchful,' making it etymologically a name for the alert and vigilant. The name entered Latin as Gregorius and was carried to prominence by a succession of saints and popes, most notably Gregory the Great (540–604 AD), the theologian and church administrator who consolidated papal authority, reformed liturgical music (giving us Gregorian chant), and dispatched Augustine of Canterbury to Christianize England.
Thirteen additional popes bore the name, and Saints Gregory of Nyssa and Gregory of Nazianzus were counted among the Cappadocian Fathers who shaped early Christian doctrine. In the secular sphere, Gregor Mendel laid the foundations of modern genetics, and Gregory Peck gave the name cinematic gravitas in the mid-twentieth century. The variant spelling Gregg — adding a second 'g' — appears in both surname and given-name traditions, associated with Scots-Irish families who carried it across the Atlantic and naturalized it in America.
The double-g spelling gained independent currency as a given name particularly in the mid-twentieth century, partly as a way of distinguishing the name visually on paper and partly through the influence of bearers like bandleader Gregg Allman, whose spelling became closely associated with a certain Southern rock authenticity. Today Gregg feels solidly vintage — a midcentury masculine name with philosophical etymology and centuries of distinguished bearers behind it.