One who drives a taxi.
It is the ending of the word that is initially of interest from the ending jis that actually means "one who is associated with". Thus we find the bagotajis – ice cream man (bagota pl. ice creams), cabaretjis, one who frequents cabarets, the loofagis who loofaris (does nothing or more colloquially "loafs around") all day and the scoubajis who collects the scoubithia (rubbish) from your house.
It is worthy of note that the jis is generally perceived as a low status individual, if not in all truth a lowlife pure and simple. You will not find a hirougajis alias a surgeon, a trabezajis – a bank worker or indeed a kivernijis – someone who works for the authorities, unless the speaker is treating them very ironically, but the taxijis - in many cases unfairly - is something of a personification of this concept, though.
He is seen as a repository of forbidden but highly desirable knowledge on the locations of all the local cabarets narcotics salespersons, crooks, thieves and thugs that any self-respecting individual might possibly want to find, hire or avoid.
With this in mind, think first whether or not you actually wish to brave the breathtaking allure of his aftershave and climb into his mercendes late at night, perhaps tipsy and possibly even alone.