For the concept, I started doing a quick sketch in Photoshop (Fig.01) (A); I wanted to make a warrior without a clear idea about the style, and I decided with a mixture of a Viking and Samurai.
 
Once the sketch was finished, I started directly on a 3D model to establish the forms. This allowed me to test various components and templates fairly quickly (B). Once satisfied with the forms and volume of the model, I created a render of the front view of the character for use back in Photoshop (C).
This last phase allowed me to sketch a rough final design. I began by studying the silhouette of the character, then doing colour tests and finally added the components and details (D).

Here's a little more detail concerning the method used in Photoshop. I begin with a solid colour and then add the shadows and lighting effects. For this I used the smudge tool to mix the colours and finished by superimposing different textures producing a subdued light across the materials. (Fig.02)

For the background I have mixed and superimposed several textures from the 3DTotal Collection.
These are the same textures that I used for the final 3D render. (Fig.03)

Hightpoly:

For the high-definition model, I am leaving my “3D Template” as it is in certain areas, and fully remodelled other elements from a cube (Polymodelling). The aim is to obtain a suitable model appropriate for ZBrush. Regarding modelling, there is nothing special here; I made a model without too many faces and a Turbosmooth applied to see the behaviour of smoothing. (you must avoid the maximum detail to have  good smoothing)) (Fig.04)

Once the model is ok, I separated it into different parts and exported it as an OBJ. I export everything into ZBrush and I begin to create all the details until the model has enough definition to extract the normal maps in 3dsmax. (Fig.05)

Lowpoly:

For the low poly version I re-imported the Zbrush meshes at a level sufficient for subdivision in order to rebuild a mesh over the low poly version. Then I need to arrange the UV’s, and this is why I unwrap the basic mesh, in order to reorganise all my UV’s and flatten them onto a 2048x2048 template (the size of my final texture.) (Fig.06)