The answer to this question does rather depend on what you mean by "prominent". The best known Roman-era slaves were those who came to public notice for some reason: gladiators, charioteers, and rebels. Of all of these celebrities, the one whose actual career as a slave we know most about is almost certainly Eunus, the rather remarkable leader of the slaves who fought in the First Servile War – a massive rebellion in Sicily in the 130s BCE that antedates the much better-known Spartacus revolt.

I wrote in detail about him in an earlier essay that will probably be is some interest to you, and so I adapt it here:

The omens had been terrible that year. In Rome, a slave girl gave birth to a monster: “a boy with four feet, four hands, four eyes, double the usual number of ears, and two sets of sexual organs,” most likely a case of Siamese twins. In Sicily, Mount Etna erupted “in flashes of fire,” spewing gouts of molten rock and scorching ash that torched rich landowners’ property for miles around.

It all pointed to trouble – to trouble in Sicily, and most of all to trouble with the slaves. And when that trouble came, it made sense of the portents, for it was the work of a slave who was in Roman eyes a monster. He was a magician who belched flames like the volcano, an adept who foretold futures, and a messianic priest-king who served a grotesque foreign goddess, and led his people in a revolt that lasted half a decade, taking five large Roman armies to put down.

His name was Eunus – which may be translated, roughly, as “the kindly one” – and although he is practically forgotten now, he was a leader fit to rank alongside Spartacus – or, in truth, above him, for while both men were slaves who masterminded wars against Rome (Spartacus six decades later), Eunus’s rebellion was four or five times as large, and it lasted something like three times as long. He built a state, which Spartacus never tried to do, and all the evidence suggests that he inspired fierce loyalty in ways the Thracian gladiator could not – after all, Spartacus (to the surprise of those who know him from romantic film and television portrayals) was undone as much by dissension within the ranks of his own army as he was by the might of the legions that were sent against him. And when the end came for Eunus, it did so in a götterdämmerung reminiscent of nothing so much as the fall of Masada, the Jewish mountain-top fortress taken by Rome around 74 A.D. At Masada, the 960 surviving defenders committed suicide en masse rather than fall into the hands of their enemies. In Sicily, the thousand picked men of the slave-king’s bodyguard hacked their way out of encirclement, only to kill one another in an identical pact when their position became hopeless – leaving their leader and his last four followers to be hunted down in the furthest reaches of the mountains that had protected them for years.

We first meet Eunus in 135 B.C. – or perhaps in 138; our sources are not precise, and we know only that the rising that he led began some 60 years after the peace that Rome imposed on Carthage at the end of the Second Punic War (218-201 B.C.) He was then the household slave of a man named Antigenes, a rich Roman who lived in the Sicilian interior; but he had been born a free man, and had been captured and brought to the island some years earlier, most likely by the Cilician pirates who ran a flourishing slave trade in the eastern Mediterranean. We know little about Eunus as a person, but the fragmentary accounts of his rebellion make it clear that he was unusually intelligent, and must have been highly charismatic. He had a reputation as a prophet, delivering predictions of the future in a trance state, and he was especially noted for something that the chroniclers who told his story present as a piece of parlour magic, but which – reading between the lines – we can reconstruct as something more impressive and portentous. He breathed out sparks and fire as he spoke, “as from a burning lamp” – an effect that he supposedly produced by concealing a hollow nut-shell with holes drilled in it in his mouth, and filling it with “sulphur and with fire.”

However Eunus produced his effects, and whether or not he truly believed himself to be divinely appointed and inspired, he was plainly an arresting character, and Antigenes used to enjoy wheeling him out at dinner parties to amuse his guests. In the course of these events, we’re told, Eunus frequently assured the assembled Romans that he was destined to be a king one day, and painted word-pictures of the ideal state that he would rule. According to the Greek historian Diodorus Siculus, Antigenes was so “taken by his hocus-pocus” that he would “cross-question him about his kingship, and how he would treat each of the men present.” When Eunus smilingly assured the masters that he would behave with moderation, the guests

“were always stirred to laughter, and some of them, picking up a nice tidbit from the table, would present it to him, adding, as they did so, that when he became king, he should remember the favour.”

The punchline of this story, naturally, is that Eunus’s prediction did come true; he did become a king, and he did come to hold the power of life and death over the Romans whom he had once entertained at the dinner table. And while the vengeance that he wrought against the slave-owning class in Sicily was truly terrible, he did remember the smirking kindness of the men who had once gifted him with bits of meat. They were permitted to live, and tell the tale of the slave who had risen to such heights.

The circumstances that brought Eunus to power had their roots in the history of the preceding decade. 

The chroniclers who wrote about his rebellion present it as something that came as an absolute surprise to the Roman citizens of Sicily, but while it seems plausible enough that a complacent group of farmers failed to spot the early signs of trouble brewing, they probably were there for those who looked for them. We know that there had been a sharp rise in the number of slaves sold in the province, as the island was turned into a bread-basket capable of feeding Rome’s fast-growing republic; wheat cultivation was highly labour-intensive, and it fuelled an insatiable demand for more and more captive workers. We know that there was a large community of Greek-speakers on the island, who could remember times when it had been more than a mere appanage of a greater state – and that there may have been as many as 200,000 slaves in Sicily in all, living on an island with a total population of no more than 600,000. We know that the conditions that most of these slaves endured were frequently atrocious; they were branded, shackled, whipped, sent out to work the fields in chain-gangs, and kept confined in their hundreds in subterranean barrack-cells known as ergastula. And we know there was resistance. Some time in the late 140s, five or six years before the rebellion began, a one-time governor of Sicily set up a stone on the mainland, a commemorative inscription in which he boasted of rounding up 917 captives who had escaped to the mainland, and of returning them to their masters. Peter Green suggests that rebellion may have been in the air for at least two or three years before it actually occurred, and that slaves in several different parts of the island probably conspired to bring it about.