Yes it is, sort of, though slavery in the ancient world is very different from what we usually think of as slavery today. The most famous banker of Ancient Athens is Pasion, active in the beginning of the fourth century. He was born a slave and worked his way up through his master’s bank . We happen to know quite a bit about his life because of the courtroom speeches of Isocrates and Demosthenes. By the time that he was running his own bank, he was a freedman and, in fact, seems to have even been granted citizenship (quite rare for foreigners). Pasion’s own slave, Phormio, was also given freedom and later ran his own bank.

So while the most famous examples of bankers that we know of had been slaves and had worked for the bank as clerks while they were slaves, they were not slaves at the time they were working as bankers. Because of the legal standing of slaves, they could not have, for example, made contracts or defended themselves in court until they were freedmen (this is made abundantly clear in the courtroom speeches).

Strange as it seems to us, in the Greek world many jobs that we would now consider high status were sometimes held by slaves (artisans, teachers, doctors, etc). Partly this was because such work required a high investment of time and money to teach the necessary skills. A young slave could be trained in these skills and then, when they got older, could pay off the debt accrued for their upbringing and training (plus however much else) to buy their freedom. The high cost of entry to these fields, coupled with the native aristocrats distaste for such work, led to quite a number of skilled professionals coming from servile backgrounds.