Adding something quickly to all cells in a column

This might be a dumb question and I apologize if it is.

I'm looking to add a comma after every name in an entire column.

So column A has 500 rows of names. Right now they read:
Smith. John

I need them to read:
Smith. John,

Is there a way to add that without having to do each one individually?

Thanks in advance.

You can also try:

=A1&","

Saves a few keystrokes.

Then you can double-click the little black box in the bottom right of the cell that contains the formula and it will fill down the formula rather than having to drag it.

Perfect! Thank you both!