With the Celts I focussed mainly on the "ancient" Celts, to fit in with Brennus and Bouddicca. Some of the modern ones could go in the English list as well I suppose, though I'd do that on a case by case basis (yes for James Watt, no for Walter Scott). The merchants are mainly petty kings who had coins minted, I'm not sure they were actually important at all, even from a "spread of currency" pov, but names at least. Also, I tried to represent all the "modern" Celtic nations of today, adding at least one representative from Cornwall, the Isle of Man, and Brittany. These people were not very important, but add a little diversity,
GP
Gennadius, Germanus, St. Alban, St. Julius, St. Aaron, Diviciacus, Lailoken, St. Deiniol, St. Gildas, St. Brigid, St. Cuby, St. Aedan, St. Maughold, Myrddin Wyllt, Adiatorix, St. David, Duns Scotus, St. Mungo, St. Melaine
GA
Favorinus, Sidonius Apollinaris, Aneirin, Taliesin, Maelgwyn Gwynedd, Bluchbardd, Cian Gwenith Gwawd, Walter Scott, James Joyce, Hywel ab Owain Gwynedd, George Bernard Shaw, Sean Connery
GSc
Marcus Antonius Gnipho, Abascantus, Marcellus Empiricus, Augustine Eriugena, Dicuil, Trogus, James Alfred Ewing, James Clerk Maxwell, Alexander Fleming, Sir Charles Lyell, Lord Kelvin
GE
Bellovesus, Addedomarus, Tasciovanus, Offa, Dubnovellaunus, James Nasmyth, James Watt
GM
Tincomarus, Agroecius, Indutiomarus, Vindex, Biatec
GG
Epaticcus, Togodumnus, Riothamus, Cassivellaunus, Viriathus, Urien, Bolgios, Lutarius, Leonnorius, Calgacus
GSp
Casticus, Commius, Orgetorix, Liscus, Acco, Aelianus, Crixus, Oenomaus, Llofan Llaf Difo, Casticus, Bobby Sands, Eamon Broy