“A colleague keeps undermining me”

What could be going on

Envy: Fits if it got worse as you gained visibility, praise or a role they wanted.

Envy disguised as critique: Constant critique that is really envy fits if the criticism is vague, personal and persistent.

Status motive: Fits if you compete for the same rank, budget or boss's attention.

Machiavellianism: Fits if it is strategic: done to the right audience, deniable, and smooth face to face.

Social comparison: They may be measuring themselves against you; check whether they track your results closely.

Confirmation bias: Check the evidence; once you suspect someone, neutral comments start to look like attacks.

Also said as

• my coworker is sabotaging me
• she keeps making me look bad in front of the boss
• he questions everything I say in meetings to make me look stupid
• why is my colleague trying to get me fired
• coworker trying to make me fail
• my colleague backstabs me to management