Here’s the Valerius Nigrinus you can actually pin down in Britain:

• Who? A Roman auxiliary cavalryman named Valerius Nigrinus, recorded on a sandstone altar. He identifies himself as a duplicarius (a double-pay sub-officer in a cavalry turma, effectively the deputy to the decurio). (Roman Inscriptions of Britain)
• Unit: ala I Tungrorum (a cavalry regiment recruited from the Tungri of the Lower Rhine). (Roman Inscriptions of Britain)
• What he did: Dedicated an altar “To Hercules Magusanus” (a Romano-Germanic god closely associated with Batavians and Tungri). (Roman Inscriptions of Britain)
• Where found: Near Mumrills fort on the Antonine Wall (Polmont parish), discovered in 1841 while building the Edinburgh–Glasgow railway; now in the National Museum of Scotland. (Roman Inscriptions of Britain)
• When: Context-dated to AD 140–165 (the Antonine occupation of Scotland). (Roman Inscriptions of Britain)

Why it matters:
This single stone shows a Tungrian cavalryman on the Antonine frontier bringing his Lower-Rhine cult with him—the kind of cultural “mix” you often see with auxiliaries posted far from home. (Roman Inscriptions of Britain)

Text (RIB 2140, Mumrills):
Herculi Magusano sacrum Val(erius) Nigrinus duplicarius alae Tungrorum — “Sacred to Hercules Magusanus: Valerius Nigrinus, duplicarius of the Cavalry Regiment of Tungrians (set this up).” (Roman Inscriptions of Britain)

About the rank “duplicarius”:
A duplicarius/duplarius received double rations/pay and typically served as second-in-command of a turma. (Wikipedia)

Any other Valerii Nigrini?
Yes—the name isn’t unique. A Valerius Nigrinus also appears on a name-list from Virunum (Noricum, modern Austria), dated broadly AD 151–230. There’s no evidence it’s the same man; it just shows the name combination occurs elsewhere in the empire. (EDH)

Roman Britain — all occurrences

• Valerius Nigrinus — duplicarius of ala I Tungrorum; dedicant of the altar to Hercules Magusanus from Mumrills (Antonine Wall); RIB 2140. Roman Inscriptions of Britain
• Marcus Cocceius Nigrinus — imperial procurator; altar to Brigantia; Hadrian’s Wall area (often linked to Brampton/Castlesteads); RIB 2066. Roman Inscriptions of Britain+1
• Nigrinus — amphora maker’s mark “(product) of Nigrinus,” York (Eboracum); RIB 2493.50–51. Roman Inscriptions of Britain+1
• Nigrinus — owner’s graffito on coarseware, Vindolanda (early 2nd c.); Brit. 36.63; also indexed as a person in RIB. Roman Inscriptions of Britain+1
• Cessaucius Nigrinus (?) — duplicarius, named on the Vindolanda tablet Tab.Vindol. 312 (reading marked uncertain). Roman Inscriptions of Britain
• Nigrina (fem.) — funerary stone, set up by a centurion of Legio VI Victrix, Great Chesters (Aesica); RIB 1746. Roman Inscriptions of Britain+1

Elsewhere in the Empire — securely attested examples

• Gaius Avidius Nigrinus — senator, suffect consul AD 110; executed AD 118 in Hadrian’s purge. (Prosopography/encyclopedic summary.) Roman Inscriptions of Britain
• Marcus Cornelius Nigrinus Curiatius Maternus — senator & general, suffect consul AD 83, later legatus of Syria; sometimes seen as Trajan’s rival. Wikipedia
• Gaius Marius Nigrinus — civic notable from Ausa (Vic), honored at Tarraco; statue-base inscription (CIL II² 14/2, 1152) notes he was flamen of Hispania Citerior; text preserved by MNAT. Google Arts & Culture+1
• Valerius Nigrinus — listed on a civic name-roll from Virunum (Noricum) (EDH HD049755). EDH
• Ulp(ius) Nigrinus — appears on a curial list from Savaria (Pannonia Superior) (EDH HD074502).