There are many ways to do that.

Can you make a list of your guids and display value for each of them? If that's the case, I think using a value list is the simplest approach.

var list = grid.DisplayLayout.ValueLists.Add();

list.ValueListItems.Add(value, name);

column.ValueList = list

 My problem is that i have this column that is called Terminated By

A task can be terminated by an employee OR a crew for example. which are both GUID. 

 So how can I achieve to show the employee name or a crew name in that column ..... instead of the GUID.  I also have another column that enable to specify by what type of operator has terminated the task, an employee or a crew, and then when going to the Terminated By column, it opens a combobox of a list of values of employee or crew depending on your choice.

Is this possible?

 I tried using the valuelist. When the combo shows, it shows the name of the employee for example, but when the employee is selected, it shows the GUID in the grid ..... 

That's strange... Make sure you put the value and text in the correct order.

About showing employee or crew, get two lists of employees and crew and add all values to the value list. You can also use a BindableValueList so you can skip the manual values insert.

Is the the appropriate way to use the BindableValueList :

 _grid.DisplayLayout.Bands[ChildBandRowKey].Columns[columnKey].ValueList = bindableValueList.ValueListItems.ValueList;

It doesn't seem to work ... I prolly got it wrong

Just set ValueList = bindableValueList