Activity Monitor won't leave dock

I put my mouse over Activity Monitor Icon on the doc and I clicked on it holding for two seconds, black drop down menu opened where I had a choice to click : QUIT

And Activity Monitor Icon was gone from my doc...

Hello:

Open Activity Monitor. Go to the menu bar>view>dock icon. Check show application icon. That will obviously disappear when the application is closed.

Barry

I could not uncheck the "show application icon"

Please let me know if this works for you - I was able to remove another icon from the doc the same way