Ara has no star bright or distinctive enough to have earned a proper name in any tradition, ancient or modern, an unusual gap for one of Ptolemy's original forty-eight. What the altar lacks in named stars, it makes up in what happens to be sitting inside its borders.
NGC 6397 lies within Ara, one of the closest globular clusters to Earth at roughly 7,800 light years away, a dense ball of several hundred thousand ancient stars packed into a volume only a few dozen light years across. Its closeness makes it one of only two globular clusters, along with Messier 4 in Scorpius, near enough for astronomers to study its individual stars in detail rather than only its overall glow, work that has helped establish how the oldest stars in the galaxy actually age.
That the cluster sits in a constellation with no bright named star of its own is a small irony worth noting: ancient observers charting the sky by eye had nothing here to single out, since a globular cluster at that distance is a faint smudge rather than a point of light, while modern telescopes found in the same patch of sky one of the most scientifically useful objects of its kind precisely because it is unusually near.
The altar's smoke, read by some ancient writers as the nearby Milky Way itself, was always the more visible feature of this stretch of sky than any single star in it.