Who invented the hand grenade during World War 1?

The Hand Grenade was invented by the Chinese during the Song Dynasty. Clay or metal pots were filled with gunpowder, a fuze was lit and the bomb was thrown. Over time, improvements were made, some were effective, some not so much. William Mills is credited with developing the first modern time-fuzed grenade. The Mills Grenade Bomb was used extensively during WW1.