This is the Mercenary Peltast with Thureos that first appeared in the Miniature Figurines 72/73 catalogue as PB 10s and subsequently in the 75 catalogue as PB 10.
Both PB ranges were based on Phil Barker's books Armies of the Macedonian and Punic Wars and Armies and Enemies of Imperial Rome. This figure is taken from illustration 10 in AMPW.
The 's' designation was used to distinguish the newer 25mm style of models from the preceding, smaller 1/72nd range. The transition was soon complete and the 's' - special - was dropped from the figure codes thereafter.
The base is stamped PB 10 on the upper surface in the usual manner.
The 'Thureos' in question refers to the type of shield - which Minifigs have depicted as a plain longish shield rounded at top and bottom. Troops armed in this fashion with spear and light javelins, and sometimes wearing mail armour, were a broad and common category of soldiery in later Hellenistic armies.
I have quite a few of these painted many years ago but only recently acquired a few unpainted examples. It's a figure that features in many contemporary collections and which turns up fairly commonly on the second hand market.
I'm thinking this chap wouldn't look out of place alongside my Spanish Scutari - the shield is almost identical and the helmet rather generic.