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I see that hundreds of students are doing PhDs at my PhD school.
What will ultimately set those PhDs apart in the academia?
NOTE: Lets, for the sake of argument, assume that quality of the papers is sufficiently high but not ground-breaking.
There are a lot of factors and many of them can't be measured simply.
Luck: They got hired at "just the right moment in just the right place"
Drive: Some people give up "life" for constant striving in research or whatever led to their success.
People: The managed to join or put together a productive circle of collaborators.
Personality: Others were happy to boost them and there was mutual admiration.
Luck again: They just happened into a hot area at the moment and made the most of it.
Luck again: They publish a paper that just happens to be seminal for the understanding of some important subfield, perhaps newly important.
Sharing: They weren't selfish about things, talked to a lot of people and shared a lot of ideas.
Speaking: They got heavily involved in conferences as speakers and eventually as committee.
Since you mention CS, I could probably name names for most of these aspects. Some designed languages that became important. Some designed various techniques, say in algorithmics or software engineering.
Just adding to the existing answer, these days it is a very important skill to be good at winning funding, grant applications and the like. Apart from the track record of past work, this requires knowing a field well, having good and realistic ideas for research, a good knowledge or assessment of what kind of thing works for what application, and the talent to present them in the way that is required to convince the funders (and maybe good qualified help by experienced people).
Also, to stress one of @Buffy's points, networking helps big time. By which I don't mean being nice to people at cocktail parties, but rather presenting your work and communicating with people who do related stuff in a qualified manner, regarding collaborations or just to make yourself known; somebody at some point may be aware of opportunities and can tell you if they know you and have an idea what you are about. This includes research visits or longer stays abroad and the like.
The obvious response is
Gender and race
The fact that it is not the first thing coming up from academians is a clear indicator how this is a poorly understood issue. See the evident living example of (ex-)Prof. Christopher Jackson or the statistics coming from Germany, where the 35% of completed PhD identifying as women are matched by a ~20% of people identifying as women have the Professor title.
