Quite an enthusiastic character, Ludo Bagman, a previously famous Quidditch player, is now the Head of the Department of Magical Games and Sports. In the beginning, he simply seems to be energetic and kind, when he tries out the Weasley twins’ fake wands with the air of a small boy opening presents at Christmas, when he offers to help Harry with the tournament, or when he describes the planning of the Quidditch World Cup extremely excitedly. At first, he is shown as a keen and fanatical character without many problems. However, like many other characters in the book, he is revealed eventually to have a deeper past.
As discovered a mere few pages before the very end of the book, Ludo Bagman got into trouble with the goblins, borrowing lots of money from them but not being able to pay it back, meaning that he couldn’t pay the Weasley twins their money back from their bet on the Quidditch World Cup. Bagman then puts a bet on Harry saying that he will win, which is why he tried helping Harry throughout the tournament the whole year, even though it was against the rules to do so. Unfortunately, the goblins said that they won the bet, because Harry drew with Cedric in the tournament, so Bagman had to run away.
Not only this but Bagman was also accused of passing on information to Voldemort’s supporters a long time back. However, he was able to be proven innocent, much to Mr. Crouch’s dislike– also to (the real) Mad-Eye Moody’s, who hated it when anyone charged with being connected to Voldemort was set free.