Since I have a good memory, I remembered and/or looked up a few names of Roman citizens who lived in Gaul or Britain or came from Gaul or Britain to other parts of the empire, and who wrote. These writers could be in ancestry anything from 100 percent Roman, or Spanish, or Egyptian, or Syrian, or Greek, or whatever, to 100 percent native Gauls or Britons descended from Celts. Probably most of them were of highly mixed ancestry.
Decimus or Decimius Magnus Ausonius (/ɔːˈsoʊniəs/; c. 310 – c. 395) was a Roman poet and teacher of rhetoric from Burdigala in Aquitaine, modern Bordeaux, France. For a time he was tutor to the future emperor Gratian, who afterwards bestowed the consulship on him. His best-known poems are Mosella, a description of the river Moselle, and Ephemeris, an account of a typical day in his life. His many other verses show his concern for his family, friends, teachers, and circle of well-to-do acquaintances and his delight in the technical handling of meter.
Gaius Sollius Modestus Apollinaris Sidonius, better known as Saint Sidonius Apollinaris (5 November of an unknown year, c. 430 – August 489 AD), was a poet, diplomat, and bishop. Born in Lugdunum (present-day Lyon, France), Sidonius is "the single most important surviving author from fifth-century Gaul" according to Eric Goldberg. He was one of four Gallo-Roman aristocrats of the fifth- to sixth-century whose letters survive in quantity; the others are Ruricius bishop of Limoges (died 507), Alcimus Ecdicius Avitus, bishop of Vienne (died 518) and Magnus Felix Ennodius of Arles, bishop of Ticinum (died 534). All of them were linked in the tightly bound aristocratic Gallo-Roman network that provided the bishops of Catholic Gaul. His feast day is 21 August.
Alcimus Ecdicius Avitus (c. 450 – February 5, 517/518 or 519) was a Latin poet and bishop of Vienne in Gaul. His fame rests in part on his poetry, but also on the role he played as secretary for the Burgundian kings.
Avitus was born of a prominent Gallo-Roman senatorial family related to Emperor Avitus.
Ruricius I (c. 440 – c. 510) was a Gallo-Roman aristocrat and bishop of Limoges from c. 485 to 510. He is one of the writers whose letters survive from late Roman Gaul, depicting the influence of the Visigoths on the Roman lifestyle. He should not be confused with his son-in-law, Saint Rusticus (Archbishop of Lyon).
Magnus Felix Ennodius (473 or 474 – 17 July 521 AD) was Bishop of Pavia in 514, and a Latin rhetorician and poet.
He was one of four Gallo-Roman aristocrats of the fifth to sixth-century whose letters survive in quantity: the others are Sidonius Apollinaris, prefect of Rome in 468 and bishop of Clermont (died 485), Ruricius bishop of Limoges (died 507) and Alcimus Ecdicius Avitus, bishop of Vienne (died 518). All of them were linked in the tightly bound aristocratic Gallo-Roman network that provided the bishops of Catholic Gaul. He is regarded as a saint, with a feast day of 17 July.
Some of the above might possibly be ancestors of Charlemagne, and thus of millions of contemporary people.
Pelagius (c. AD 360 – 418) was a theologian of British origin who advocated free will and asceticism.
Because Palagius was accused of heresy, most of what is known about his teachings comes from hostile comments by his opponents.
One of the poems of Ausonius attacks a rival poet, Silvius Bonus from Britain, in a poem saying that it is a contradiction in terms for a Briton to be Bonus (good).
It has been suggested that Silvius Bonus could have been a relative of Vortigern.
Anyway, those are the first few names I remembered or could dig up.