Final answer:
Jerome Kerviel was the Societe Generale employee responsible for committing a massive fraud resulting in a loss of around €4.9 billion.
Step-by-step explanation:
The Societe Generale employee alleged to have committed fraud against the firm, resulting in a loss to the bank of approximately €4.9 billion, was Jerome Kerviel.
This case is one of the largest trading fraud scandals in history, where Kerviel was charged with forgery, breach of trust and unauthorized use of the bank's computers. His unauthorized trades in 2007 and 2008 far exceeded his risk limits and created exposure to the bank that led to significant financial loss once discovered.