Johannes Nicolaas Hendrik (Johan) Grobler was born on 27 February 1864 in the Lydenburg district. He moved to Ermelo and in 1891 he became assistant veldcornet and three years later veldcornet.
In 1899 he was appointed Commandant in the place of Tobias Smuts. He went to Natal and took part in the battles of Dundee, Modderspruit, Colensoe, Spioenkop, Bosrand and Pieters Hights. After a few battles in the Freestate he went back to the Transvaal and fought at Donkerhoek, Ermelo and Dalmanutha.
With the second attack of Natal he with the Ermelo commando fought at Melmoth and Itala.
A day after the battle of Bakenlaagte on 23 October 1901 he was promoted to Vecht General and keep on fighting till the peace of Vereeniging and hand over his weapon on 9 June 1902