Complex sentence: Richard Solomon, usually known as Dick Solomon, (John Lithgow), is the High Commander of a highly trained alien unit, on the late 90's NBC "3rd Rock from the Sun", sent to Earth by their leader The Big Giant Head.
Split into simpler sentences: Richard Solomon, usually known as Dick Solomon, is a character played by John Lithgow in the late 90's NBC sitcom "3rd Rock from the Sun". Solomon is the High Commander of a highly trained alien unit, sent to Earth by their leader, The Big Giant Head.