Interval comes from Latin “intervallum”.
The intervallum was a property of the Roman fort. The Romans left free space between (“inter”) the outer wall (“vallum”) and the buildings inside, so that arrows or other projectiles would land in this free space, doing no damage.
Kim Scott claims in “Radical Candor” that the phrase “rock star” in reference to developers was coined at Apple, and not with the current meaning of some extremely productive developer, but as a contrast to “super star”.
Where the super star is on an explosive career trajectory, always changing jobs, the rock star gets this name from the proverbial rock. The rock star is extremely good, as well, but doesn't aim for his boss's position and is content with his rank.
For team dynamics the rock star is very important as a source of stability.