Empress Lü Zhi
In his later years, Emperor Gaozu favoured Concubine Qi and neglected Empress Lü Zhi. He thought that Liu Ying, his heir apparent (born to the empress), was too weak to be a ruler. Thus, he had the intention of replacing Liu Ying with another son, Liu Ruyi, who was born to Concubine Qi. Lü Zhi became worried, so she asked Zhang Liang to help her son maintain his position. Zhang Liang recommended four reclusive wise men, the Four Whiteheads of Mount Shang, to help Liu Ying.