PARIS  Jérôme Kerviel was too middling to be considered a loser. Until he was charged by Société Générale with perpetrating the biggest fraud of its kind in banking history, there was nothing superlative about him.

He failed in a bid for town council in his 20s; he never rose higher than a green belt, a midlevel rank, after years of judo training  because of his bad knees; and he attended an average college where he earned respectable but unremarkable grades.

“People who want to be golden boys or clever in the market don’t come here,” said Valérie Buthion, the director of the University of Lyon’s economic and financial engineering department, where Mr. Kerviel earned a master’s degree in market finance. “The showoffs don’t come.”

As they sought to explain how a low-level trader caused a $7.2 billion loss, Mr. Kerviel’s former bosses at Société Générale, one of France’s oldest and most venerated banks, portrayed him as a “brilliant” trader who eluded sophisticated detection systems.