Usopp's name is probably based on "Isoppu", which is the Japanese pronunciation of Aesop, the ancient African fabulist, who lived in Greece. Considering that "uso" means "lie" in Japanese, the name Usopp can (and is most likely meant to) be taken as a portmanteau name between uso and Isopp, both defining a liar or teller of tall tales (for example, when introducing himself, Usopp is known to say "Ore wa Usopp!" which can mean either "I am Usopp!" or "I am a liar!"). Usopp's long nose is an allusion to Pinocchio, a wooden boy who possessed a nose that would stretch after he lied. His nose is nine inches long, and according to Mr. 2 Bon Clay's standards, Usopp possesses the world's weirdest/funniest nose.
The other aspect of Usopp besides his lying is his cowardice; he is a very timid person, or so he thinks. (He is constantly ailed by illnesses such as I-can't-go-on-that-scary-island disease.) In extremely stressful situations, Usopp has proven to be far more courageous than he believes himself to be. He shows great resolve when his friends are threatened or mocked by outsiders. Even though he is a complete coward in battle (except as his alter ego, Sogeking), he is a useful part to the Straw Hat Pirates. He is extremely handy and can fix almost anything. He is also a talented artist, a skill he claimed he got drawing on walls as a kid.
Despite his lack of physical strength compared to other members of the crew, Usopp seems to be just as resilient (if not more so) as his comrades. He suffers injuries in almost every fight he participates in, but shrugs them off after a very short period of time. Part of this is the result of care by the Straw Hats' very capable doctor, yet some of this appears to be a natural ability to absorb punishment, for the sake of comedy relief. (Indeed, he once was hit in the head by Mr 4's 4-ton baseball bat, only to stand up seconds later. Miss Merry Christmas commented that he should not even be alive.)
His goal in life is to become a proud and strong pirate like his father Yasopp of the Red Haired Pirate Crew.