(ORIGINAL LAST NAME - GERVAIS)
The legendary jewel thief "Doc" Villaroche - like his daughter Krista many decades later, was using an alias based on his mother's maiden name. He did so at the request of his brother Victor, who still bore the family surname of Gervais.
Victor Gervais was a section head for THRUSH, but he was not demanding his brother change his name out of resentment for Doc's chosen profession. Rather, he was thinking of his brother's safety should their familial relationship ever be discovered by the enemies of THRUSH. More than a decade later, this concern would be even more necessary once Doc had a daughter, Krista.
So Doc chose the maiden name of their mother, Christianna Villaroche, and he had to admit... "Doc" Villaroche had a certain panache that could not have been matched had he remained "Doc" Gervais. In later decades a name like that would have better fit into the jazz club scene.
(Victor Gervais would not always remain by his birth name, however. He went into business for himself as a double agent, known as Kinsey Krispin. Krispin used a factory for creating mass-produced statuary as a cover; but an on-site accident caused him to fall into one of the vats. This left him with his skin permanently disfigured as chalky white in coloring and his hair tinted a minty green. That unbalanced his mind and he would forever after be more famous - or rather infamous! - as the Clown Prince of Crime, the Joker......)
Why the name of "Christianna" for the mother of Victor and Doc? Because I liked the idea that Doc would name his daughter with a variation of his own sainted mother's name. Krista from Christianna. And its Mediterranean flavor flowed well with "Villaroche Gervais"......
As for Doc's real first name? I'm sure there are any number of one-shot characters played by Cesar Romero in his later years without so much back-story. We could claim one of them was an alias Doc adopted when the world thought him dead. (And with an alias, it's always advisable to use your real first name so that it's easy to remember.)
Romero's starring role as Peter Stavros of 'Falcon Crest' and the one-shot appearance on 'Murder, She Wrote' as the painter Diego Santana would have to be excluded as they have too much back-story. The same for any other murderers or murder victims he may have portrayed on TV over the years.