How to group by DESC order

I have the following table called questions:

ID | asker 
1  | Bob
2  | Bob
3  | Marley

I want to select each asker only once and if there are multiple askers with the same name, select the one of the highest id. So, the expected results:

ID | asker 
3  | Marley
2  | Bob

I use the following query:

SELECT * FROM questions GROUP by questions.asker ORDER by questions.id DESC

I get the following result:

ID | asker 
3  | Marley
1  | Bob

It selects the first 'Bob' it encounters instead of the last one.