Ludovic Bagman is a former Quidditch player who later joined the Department of Magical Games and Sports at the Ministry of Magic and eventually became head of the department. When he was a beater for the Wimbourne Wasps (a league Quidditch team) he was supposedly quite good-looking with blond hair and blue eyes. Since his Quidditch days, he has put on weight and now has a squashed nose, possibly from being hit by a bludger.
He was accused of being a Death Eater during the first war because he passed information to Augustus Rookwood. Rookwood, a friend of Bagman’s father, was later named as a Death Eater by Igor Karkaroff during his trial. Rookwood was the person who helped Bagman get his Ministry job and was famous for his network of spies in the Ministry. Bagman was acquitted because he did not know that Rookwood was a Death Eater and assumed he needed the information for Ministry work.
His main role in the books is as a chronic gambler. When we first meet him in book four he makes a bet with Fred and George Weasley on the outcome of the Quidditch World Cup. After losing a multitude of monetary bets he resorts to paying off his debts in Leprechaun Gold, which disappears after a short period of time. Throughout the book, Fred and George attempt to claim their winnings from him by constantly writing to him and eventually trying to confront him when he comes to Hogwarts for the Triwizard Tournament. Bagman successfully avoids the twins for a period of time, however finally tells them that they were “too young” to be gambling and refused to give them any money.
Bagman also owed money to goblins, who tried to reclaim their winnings by cornering him in the woods outside the stadium where the Quidditch World Cup was taking place. They took all the gold he had on him but it wasn’t enough to fully cover his debts. He placed a bet that Harry would win the Triwizard Tournament and then used his power as a judge to ensure he would win. He constantly gave Harry advice and gave Harry a perfect score during the first task, which Harry clearly didn’t deserve.
After the Triwizard Tournament, the goblins claimed that since Harry had tied with Cedric Diggory, Bagman technically didn’t win, hence Bagman lost his bet and still owed them money. Bagman fled after the third task of the tournament and hasnt been mentioned since. His current location is unknown.