1. Set the GridView column’s 'Visibility' property to 'False'. However in this case, GridView will not bind the data to the GridView. So if you want to use that hidden column (like a Master-Detail scenario), you won't be able to do it.
You can also hide the column programmatically in the RowDataBound event
2. Use the OnRowCreated event which gets called after the data is bound
Using this way, you can use a hidden column's data even if it is hidden.