I have a colleague who prioritizes maintaining control over teaching others. He tries to force a particular perspective, emphasizing the importance of his role

I have a colleague who prioritizes maintaining control over teaching others. He tries to force a particular perspective, emphasizing the importance of his role while fostering dependency rather than sharing knowledge. This seems driven by a fear of losing his job. My primary focus is backend development, where I assist developers and solve infrastructure challenges. However, I’m so effective in this role that I often end up boxed into it. I’ve been making an effort to expand into frontend development to broaden my expertise, but this colleague operates in that space and isn't the only one who has made it difficult for others to gain traction.