Who is Gulliaume 'G' Lenotre from Revolution and what is their importance?

Gulliaume 'G' Lenotre is a historian and author. G and Lewis roomed together in college and remain good friends, even though they don't often see eye to eye on a great number of topics. When Lewis visits Paris over winter break, he works with G to do DNA on a heart thought to belong to Louis-Charles, the lost king of France. G also provides Andi with background on Louis-Charles as well as information about Amade Malherbeau, the topic of her senior thesis. Through G, Andi finds Alex's diary because it is in a guitar case that G bought to display in a museum on the French Revolution.