Complex sentence: Albert Gallatin Mackey (March 12,1807--June 20,1881) was an American medical doctor, and is best known for his authorship of many books and articles about freemasonry, particularly Masonic Landmarks.
Split into simpler sentences: Albert Gallatin Mackey (March 12,1807--June 20,1881) was an American medical doctor and author. He is best known for his writing many books and articles about freemasonry, particularly Masonic Landmarks.