a rough diamond¹ 

a diamond in the rough

If you refer to someone, especially a man, as a rough diamond, you like and admire them because of the good qualities they have, even though they are not very sophisticated or well-mannered. This form of the expression is used mainly in British English; in American English, the usual form is a diamond in the rough.

Marden was the rough diamond of the three, feared for his sardonic ruthlessness respected for his First World War Military Cross.

`The character I'd like to have met,' Stanley Marric said, `was Arthur Crook. I could really identify with a rough-diamond kind of lawyer like him.'

I liked Neil Murphy, good AA-type treatment who is somewhat of a diamond in the rough.

a rough diamond²    

a diamond in the rough

If you refer to someone or something as a rough diamond, you mean that they have a lot of talent or potential which needs hard work before it can be revealed. This form of the expression is used mainly in British English; in American English, the usual form is a diamond in the rough.

British first novels are more likely to be rough diamonds, with flashes of inspiration in an imperfect whole.

When I heard this lady sing, thought, I said `Oh, my goodness.' So I ran to the theater, I said, `Chick, I found myself a diamond in the rough.'