I'm still working on my fluff but currently my guard all fit into one of two regiments. My infantry all come from one and my armour from the second:
36th Patagan "NightHawks" - Col. Kriton
-Notable Companies:
--> A Company - Major Glade
--> B Company - Capt. Gazzala
--> E Company - Capt. Wertze (These guys are base of most of my army lists)
--> H Company - Capt. Gelding
23rd Patagan Armoured - Col. Schultzky
Basically they all hail from Planet Patagaz, a rich industrial world, which became largely corrupted by chaos, eventually forcing entire planet into civil war. The two regiments I use are ones who remained loyal to the Emperor and eventually prevailed. I haven't worked out much for the 23rd Armoured yet, but the 36th "NightHawks" are a merged Regiment of the 36th Patagan Mechanized and 116th Patagan Heavy Infantry and so comprise both mechanized and foot elements (yes I admit, just my excuse to put mech and foot guard in same regiment

). They are well equipped and well lead with high survival rates and so consist largely of veterans. All the models I use in my army lists are E or H company.