I would generally not start such a conversation without some sounding out of the topic with the boss. In the question posed there are no conditions for other colleagues, so I consider an isolated triangle - 1) the author of the question, 2) his harmful colleague, 3) their common boss. The main problem of this triangle, as a rule, is not that the colleague complains to the boss. The main problem is that the boss listens to his colleague. If, for example, the boss begins to ignore such complaints, considering them incorrect and annoying, then from that moment the colleague, instead of harming you, will begin to harm himself. After all, complaints are a double-edged sword. We must also take into account that colleagues rarely make decisions about our income or personnel movements within the organization. More precisely, strong horizontal interdependence is characteristic of a narrow list of industries such as IT. Much more often, the key figure who determines the overall meaning of our work at a given place is, in most cases, the boss. This is the main point of our influence. Of course, you cannot ask your boss a question about a specific colleague “head-on”. It is necessary, after waiting for a favorable moment, without attracting undue attention, to briefly ask your boss about his assessment of the results of your work that your colleague is criticizing. If everything is OK here, you can dig deeper and ask his assessment of your personal qualities, soft skills and dedication, since your colleague probably criticizes all of this. In addition to contacting your boss directly, I would ask other colleagues - how does he relate to your ill-wisher? Whatever results this “reconnaissance in force” brings you, you will have a much more adequate idea of ​​objective reality: If the boss is already deliberately critical of you, this is a signal that you need to act much more carefully, in “small steps.” Even if you are 100% right. If your boss values ​​your contribution and is not too focused on the opinion of a “harmful colleague” - act boldly! The main approach is cognitive behavioral therapy. Fast and efficient. Anxiety, fears, burnout, separation... Resources, meaning, new life! Online via video call 4 t.r. in 1 hour, offline Moscow (Center).