The fund manager is responsibile for the managment of the fund's investments, for its customer service activities, and for associated functions such as compliance with SEC requirements and by-laws to publish the prospectus, hold an annual meeting, issue proxies, annual reports, and negotiating for services such as broker commissions, research, etc. The fund manager may hire people to carrry out these functions or may contract with others to provide all or parts of the service.
As a practical matter, most mutual funds are owned by mutual fund companies who provide many of the services for a fee to the individual mutual funds in their family of funds.
In selecting a mutual fund, many advise one to consider the longevity of the fund manager. Recent changes in management imply dissatisfaction with performance or other issues. It may also imply a change in investment strategy. A long standing fund manager with a good performance record is an asset to a mutual fund.
Many mutual funds name an individual as the fund manager, but most large funds probably have a staff led by the fund manager. The fund manager then is often the investment manager. Some funds are managed by several managers. Some are managed by investment firms.