Senegal international Diouf, 30, said: "People call me a bad boy and I know I have got a bit of a reputation.
"But I have never been to jail and I have never done anything stupid. Now I am here to play and help Doncaster. I have certainly not come here for the money. If I'd wanted that, I would have gone to Russia or Qatar.
"I still see my future in the Premier League but my focus for the next three months at least is on helping Rovers."
Diouf has been without a club since he was released by Blackburn in June and he joins Pascal Chimbonda and Herita Ilunga - whose affairs are also managed by Willie McKay - at the Keepmoat.
Boss Dean Saunders, another on McKay's books, said: "West Ham offered El-Hadji a deal but we've persuaded him to come and play for us.
"He's a brilliant signing. He's won African Player of the Year twice which is no mean feat considering some of the players they've got over there."