Ocelus is a Celtic god

Celtic polytheism

Celtic polytheism, commonly known as Celtic paganism, refers to the religious beliefs and practices adhered to by the Iron Age peoples of Western Europe now known as the Celts, roughly between 500 BCE and 500 CE, spanning the La Tène period and the Roman era, and in the case of the Insular Celts...

 known from three inscriptions in Roman Britain

Roman Britain

Roman Britain was the part of the island of Great Britain controlled by the Roman Empire from AD 43 until ca. AD 410.The Romans referred to the imperial province as Britannia, which eventually comprised all of the island of Great Britain south of the fluid frontier with Caledonia...

. He is twice invoked on dedications at Caerwent

Caerwent

Caerwent is a village and community in Monmouthshire, Wales. It is located about five miles west of Chepstow and eleven miles east of Newport, and was founded by the Romans as the market town of Venta Silurum, an important settlement of the Brythonic Silures tribe. The modern village is built...

: one stone is the base of a state of which only a pair of human feet and a pair of goose feet survive. The invocation is to Mars

Mars (mythology)

Mars was the Roman god of war and also an agricultural guardian, a combination characteristic of early Rome. He was second in importance only to Jupiter, and he was the most prominent of the military gods worshipped by the Roman legions...

 Lenus

Lenus

Lenus was a Celtic healing god worshipped mainly in eastern Gaul, where he was almost always identified with the Roman god Mars. He was an important god of the Treveri tribe, who had large sanctuaries at medicinal springs at Trier and the Martberg by Pommern in what is now Germany. Two dedications...

 or Ocelus Vellaunus

Vellaunus

Vellaunus is a Celtic god known from only two inscriptions. The first, found at Caerwent is the base of a state recording the dedication of the statue to:...

 and the "numen" (spirit) of the emperor, and was dedicated on 23 August AD 152. The second Caerwent inscription dedicates an altar to Mars Ocelus. The god was also venerated at Carlisle, where he was once more equated with Mars and again linked to the imperial cult. So Ocelus seems to have been a British, perhaps Silurian

Silures

The Silures were a powerful and warlike tribe of ancient Britain, occupying approximately the counties of Monmouthshire, Breconshire and Glamorganshire of present day South Wales; and possibly Gloucestershire and Herefordshire of present day England...

 god, associated with Mars, probably in the latter's Celtic capacity as a protector. At Caerwent he is linked with Lenus, a Treveran healing deity, and with Vellaunus, who is recorded among the Gaulish Allobroges

Allobroges

The Allobroges were a Celtic tribe of ancient Gaul, located between the Rhône River and the Lake of Geneva in what later became Savoy, Dauphiné, and Vivarais. Their cities were in the areas of modern-day Annecy, Chambéry and Grenoble, the modern of Isère, and modern Switzerland...

.
The Caerwent inscription uses the actual name of Ocelus and reads as follows:
DEO MARTI OCELO
AEL AGUSTINUS
OP V S L M

God Mars Ocelus
Ael(ius) Agustinus
Op(tio) Paid His Vow

(VSLM stood for Votum Soluit Libens Merito)