Complex sentence: This was one of three eagles known to have been owned by Washington, who most often wore the "diamond eagle," a diamond-encrusted badge given him by the French "matelots" (sailors).
Split into simpler sentences: This was one of three eagles known to have been owned by Washington. Washington most commonly wore the "diamond eagle," a diamond-encrusted design that was given to him by the French "matelots" (sailors).