Materials

Steel

The purpose, geometry and the steel make a knife. There is no such thing as the ideal knife for all usages as there is no ideal steel for every knife out there.
In my early days as a knife maker I played around with all kinds of steels. Now I use steels from the following main groups.

Carbon steel / low alloy tool steel

Those are non stainless steels. Heat treated properly those steel have a very fine grain structure and allow for fine geometries and extreme sharpness. 

Blades from both groups need a certain care, non-stainless does not mean immediate corrosion and rust, you can prevent that by cleaning and frequent oiling of the blade. But colorization of the steel after contact with acidic foods is quite normal.
 
Carbon steel: C105, US 1095
Low alloy tool steels: 1.2842, 1.3505, 1.2235
 
Stainless steels
 
High alloy “stainless“ steels. I mainly use 2 types of stainless steels that have similar properties. The high chromium content makes it stainless but the steels also contain Niobium which leads to a very fine grain structure and allow for delicate edges. I use those steels quite a lot for kitchen knives
 
SB1/Niolox (1.4153.03)
Crucible CPM S35VN

 
Other steels
 
Once in a while I use Damascus steels. I buy those steel blanks specifically for the particular knife.
 
Stainless Damasteel
Damascus steel from Balbach (Germany)