Question
In the context of weight lifting (or resistance training), what single exercise is the most important?
Answer
The squat (according to page 7 of Starting Strength). Page 19 says "There is simply no other exercise, and certainly no machine, that produces the level of central nervous system activity, improved balance and coordination, skeletal loading and bone density enhancement, muscular stimulation and growth, connective tissue stress and strength, psychological demand and toughness, and overall systemic conditioning than the correctly performed full squat."
The power clean could be more important according to Bill Starr (in The Strongest Shall Survive: Strength Training for Football, based on what page 177 of Starting Strength says).
With long hours at the keyboard, your lower back may need strengthening. Squats can contribute to a strong lower back. We think more than one exercise is necessary to healthfully and safely enable long hours of sitting.