Can fund managers invest in their own funds?

Hi,

I am a rising junior at a liberal arts college (think top 20). I am interested in investing and am considering working for an investment fund (among other finance related paths) hopefully as a portfolio manager someday. My question is as a fund manager, can I personally invest in the stocks/equities I invest in as a portfolio manager too? Would this be considered a red flag or illegal? Let's say I invest in company X because I think it has strong fundamentals and potential but it's still somewhat risky. Nonetheless, I believe in it and therefore I invest some of my own money into it because I am willing to lose some of my own money but I am not confident enough to invest client money into it. 6 months to a year later I feel better about this company having done more research and decide to invest in it as a portfolio manager. Is this illegal?