Which coronary artery is called widow maker artery and why?

Coronary arteries are blood vessels supplying oxygenated blood to the heart muscle. LAD is short for left anterior descending coronary artery. LAD is usually the largest branch of the left main coronary artery which supplies the major portion of the left ventricle.
Hence blockage of LAD can cause a major heart attack, which can sometimes be fatal. That is why LAD has been called a widow maker artery. LAD supplies the front region of the left ventricle and the partition wall between the ventricles. Ventricles are the lower muscular pumping chambers of the heart.
When the LAD is blocked at its origin, the resulting damage to the heart muscle is large so that the pumping function may fail. It can also alter the heart rhythm abruptly causing cardiac arrest or stoppage of heart function. This can lead to sudden death unless prompt chest compressions and artificial breathing, known as cardiopulmonary resuscitation or CPR is given.