You have to distinguish between those who signed the Declaration of Independence and those who wrote/framed it. George Washington was one of the main Founding Fathers - but he never actually signed the DoI for example. John Hancock was probably the most famous signatory and was the first person to sign it but did little to actually frame it other than preside over the Continental Congress that adopted it. His name has though become a synoym for a signature as he signed the document with a flourish - in America the expression "put your John Hancock here" is still used as a request to sign something.

Personally I would interpret the expression "Founding Fathers" reasonably broadly, there are four great US state papers - the Declaration of Independence, the US Constitution, the Continental Convention and the Articles of Confederation. The characters involved in drafting these documents overlapped considerably but only one man signed all four - Roger Sherman and who has heard of him? In addition there were the Federalist Papers which provided the intellectual heft for a constitution., the Treaty of Paris that negotiated the peace Treaty with Britain and other writings and events such as the War of Independence.

Historians though have anticipated your question and tend to talk of the "Key Founding Fathers" - Thomas Jefferson, Ben Franklin, George Washington, John Adams, John Jay, Alexander Hamilton and James Madison as being the most influential fathers, while there are a number of others, like Roger Sherman and John Hancock who qualify only in the broadest interpretation.