I don't know of any professional golfers who use a one iron these days. They're just not as popular as they once were. Most golfers find that they hit their other clubs (specifically, their woods and hybrids) better than their one iron, and so they don't bother carrying one around with them.
There are a few reasons for this. First, one irons are very difficult to hit well. They have a very small sweet spot, and so it's easy to miss-hit the ball and send it off-course. Second, one irons are very long - they have a lot of loft, but they don't hit the ball all that high. This can make them tough to use on certain types of shots, such as approach shots into greens.
That said, there are still some golfers who use one irons. They tend to be the more experienced players who have a good understanding of their own swing and who know how to hit the ball well with that club. If you're thinking of using a one iron, I would recommend talking to a golf professional or taking a few lessons first, just to make sure that you're using the club correctly.
