Louis Blanchard was a Human raised in France on Earth in the early 24th century. He was a childhood friend of Robert and Jean-Luc Picard. Louis was the son of Doctor Henri Blanchard and was the father of Sophie Blanchard. (TNG - Starfleet Academy novel: Starfall)
Once he went on a cycling trip with the Bloom sisters Kimberly and Melissa and broke his leg on the trip, but later married both of the sisters. He was still married to one of them in 2367. Picard described Louis as a "desperately poor swimmer."
In 2367, Louis was the supervisor of the Atlantis Project. Shortly after Picard was liberated from the Borg, Louis wanted him to take lead of the project and even arranged a meeting with government officials for him, but ultimately Picard cancelled the meeting and declined the offer. (TNG episode: "Family", TNG novel: Perchance to Dream)
In 2375, during the Dominion War, the Dominion took interest in the Atlantis Project and a Vorta was later sent with Jem'Hadar and Breen soldiers to interrogate the personnel of the project, including Louis. (TNG short story: "Solace in Bloom")