Willgodt Theophil Odhner is a Swedish engineer and entrepreneur, working in St. Petersburg, Russia.

He is the inventor of the Odhner Arithmometer, which by the 1940s is one of the most popular type of portable mechanical calculator in the world.

According to a brochure distributed by Odhner's company at the Paris World exposition of 1900 "...Odhner had, in 1871, an opportunity to repair a Thomas calculating machine and then became convinced that it is possible to solve the problem of mechanical calculation by a simpler and more appropriate way".

It takes him 19 years to perfect the design of this new machine so it can be manufactured effectively.