Who were the four great calligraphers in Tang Dynasty?

There were many famous calligraphers in the Tang Dynasty, four of which were Ou Yangxun, Yan Zhenqing, Liu Gongquan and Zhao Mengfu.

Ou Yangxun was a famous calligrapher in Tang Dynasty. His calligraphy is famous for regular script, and he is known as one of the "four masters of regular script". Yan Zhenqing was a famous calligrapher in the middle Tang Dynasty. His calligraphy is famous for running script and regular script, and is regarded as one of the founders of Yan calligraphy. Liu Gongquan was a famous calligrapher in the late Tang Dynasty. His calligraphy is famous for regular script, and he is known as one of the founders of "six-style" calligraphy. Zhao Mengfu was a famous calligrapher in Yuan Dynasty. His calligraphy is famous for regular script and running script, and is known as one of the "four masters of regular script".