Ole Herman Johannes Krag (7 April 1837 – 9 December 1916) was a Norwegian officer and firearms designer.

In 1866 he was ordered to Kongsberg Våpenfabrikk, the most important Norwegian weapons factory of its day.

Ole H J Krag constructed his first repeating rifle in 1868, which evolved into the Krag–Petersson (aided by Axel Petersson) by 1872.

This, as well as his work in the armoury, gave him a thorough understanding of what requirements the Norwegian Army had to a rifle, allowing him to create the successful Krag–Jørgensen with the help of his good friend Erik Jørgensen.

He designed a wide range of firearms during his lifetime, but only two – the Krag–Petersson and the Krag–Jørgensen – were adopted by any armed forces.