Vaclav Holek's first machine gun design for the Czech military was the Praga I, built in 1922 and based heavily on the Vickers/Maxim system. However, it became clear that the military wanted something lighter and more portable, and so the next year he heavily updated the design to this, the Praga I-23 (for 1923). It remains a belt-fed weapon chambered for the 8mm Mauser cartridge, but the locking system has been much simplified into a tilting bolt arrangement. The recoil operation from the earlier model is also gone, now replaced by a long stroke gas piston. Some elements of the Maxim remain in the belt feeding elements, but the overall gun is much more a light machine gun than the mounted heavy machine gun that was his first design.

A total of 40 of the Praga I-23 were ordered by the Czechoslovak military, and they were tested in 1924 (only 20 examples were actually delivered of the 40). The I-23 performed well, but it was again clear that it wasn't quite what the military really wanted. Holek revised the design again to the model 1924, using a box magazine instead of a belt feed - and that is the gun that continued the path to the ZB-26.

Video on the Praga I machine gun that came immediately before this model:
https://youtu.be/ByZvMvBnefo

Many thanks to the VHU - the Czech Military History Institute - for giving me access to this fantastic prototype to film for you. The Army Museum Žižkov is a part of the Institute, and they have a 3-story museum full of cool exhibits open to the public in Prague.If you have a chance to visit, it's definitely worth the time! You can find all of their details (including their aviation and armor museums) here:

https://www.vhu.cz/en/english-summary/