SQL Server Agent is a Microsoft Windows service that allows you to automate various MSSQL administrative tasks, which are called jobs. SQL Server Agent uses SQL Server to store job information. Jobs contain one or more job steps. Each step contains its own task, for example, backing up a database. SQL Server Agent can run a job on a schedule, in response to a specific event, or on demand. For example, if you want to back up all the company servers every weekday after hours, you can automate this task. Schedule the backup to run after 22:00 Monday through Friday; if the backup encounters a problem, SQL Server Agent can record the event and notify you. If you disable this service, then any scheduled MSSQL tasks will not run.
As such, you must start the SQL Server Agent (MSSQLSERVER) service before your local or multiserver administrative tasks can run automatically. SQL Server Agent runs as a service called SQL Server Agent (MSSQLSERVER), if it is the default instance, or SQLAgent$, if it is a named instance. IF MSSQL is installed as a named instance, its name will reflect the version of MSSQL being installed or the program that is using it. For example, other Service Names you may see include SQLAgent$SQLDEVELOPER, SQLAgent$SQLSERVER2008, SQLAgent$DEVELOPER2008, SQLAgent$AUTODESKVAULT, SQLAgent$MICROSOFTSMLBIZ, SQLAgent$PINNACLESYS, SQLAgent$SONY_MEDIAMGR, SQLAgent$VAIO_VEDB, SQLAgent$SQLEXPRESS, etc.
The files for this service may be installed a variety of different paths, which may include the MSSQL version number.