The question lists What they're doing but barely speculates as to Why, beyond "to look good."
Most people I've seen treated this way get it because they've either badly or repeatedly screwed over colleagues.
From the description, it's an environment where people don't have much trust in management/HR helping. In such a situation, where the gaslighter may well have a legitimate issue with the victim but, in the absence of legitimate channels, taking away their ability to succeed until they go away remains an apparent only choice.
So first step is to consider if you've screwed then over. Not by your definition but by theirs. If so, start by mending bridges.
Maybe it is nothing to do with the victim. Still ask why.
Maybe they're a very insecure person, despite the rockstar talents the victim perceives.
Maybe they're scared of someone less talented but younger and hotter.
Or maybe they're hurting from other bad workplace drama, a bad manager, another bullying colleague, and lashing out where they can.
Get to know them, understand them, empathize, build their trust, make yourself an ally they want to build up not tear down.
Is that fair? Should you have to work with an unfair bully?
No. Back when mommy could talk to the teacher, it wasn't fair.
But this is the real world. In a good company, management and HR will help but this apparently isn't one. That leaves leaving (hurts you), fighting (often hurts you more) or being the bigger person to ensure you succeed.
You're going to hit lots of unfair in your career. Working out how to win anyway is at least as important a skill as any technical one.