The back of Quests & Campaigns has a random religion chart, either to be used on its own or as part of character background generation using Ultimate Campaign. As noted in this thread, a completely random religion does not mesh with all alignments - especially for clerics and paladins. I created a method that incorporated the Conflict Points detailed in Ultimate Campaign, but that method only listed the main 20 deities of the Pathfinder system.
Here's a new subsystem for those using the myriad divine entities of the Inner Sea (requires Ultimate Campaign):
Once Conflict and Motivation are determined, but before Resolution is, roll on these tables:
Basic Faith (d20)
1-15: Dedicated
16-19: Undecided
20: No Deity
Undecided and No Deity are as written. If Dedicated, roll on the following table, with an adjustment based on your CP. If your result is higher that 20 or lower than 0, reroll.
2-3 CP: +34
4-7 CP: +12
8-12 CP: +0
13-15 CP: -13
16-18 CP: -31
Dedicated Faith (d%)
Chaotic Evil
01-04: Rovagug
05-08: Lamashtu
09-10: Demon lord
11-12: Other Chaotic Evil deity, Eldest, or forgotten deity
Neutral Evil, Chaotic Neutral
13-16: Norgorber (NE)
17-20: Urgathoa (NE)
21-24: Gorum (CN)
25-28: Calistria (CN)
29: Neutral Evil or Chaotic Neutral Other deity or Eldest
30-33: Elemental lord (NE), Horseman (NE), or forgotten deity (CN)
34: Philosophy, the Whispering Way
Lawful Evil, Neutral, Chaotic Good
35-39: Zon-Kuthon (LE)
40-43: Asmodeus (LE)
44-47: Nethys (N)
48-51: Pharasma (N)
52-55: Gozreh (N)
56-59: Cayden Cailean (CG)
60-63: Desna (CG)
65: Other deity (LE, N, CG)
65-66: Archdevil (LE)
67: Eldest, Empyreal lord, forgotten deity (LE, N, CG)
68: Philosophy, diabolism (LE)
69: Philosophy, the Green Faith (N)
Lawful Neutral, Neutral Good
70-73: Irori (LN)
74-77: Abadar (LN)
78-81: Shelyn (NG)
82-85: Sarenrae (NG)
86: Other deity, Eldest, Empyreal Lord (LN, NG)
87: Philosophy, the Prophecies of Kalistrade
Lawful Good
88-91: Torag
92-95: Iomedae
96-99: Erastil
00: Other deity, Empyreal lord (LG)
Then, choose your Conflict Resolution based on your faith.
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Demon Lords (CE) (d%)
01-07:Abraxas
08-14: Angazhan
15-21: Baphomet
22-28: Cyth-V'sug
29-35: Dagon
36-42: Deskari
43-49: Gogunta
50-56: Kostchtchie
57-63: Nocticula
64-70: Orcus
71-77: Pazuzu
78-84: Shax
84-91: Socothbenoth
92-98: Zura
99-00: Other (find a different Chaotic Evil demon lord or roll again)
Other deity, Eldest, forgotten deity (CE) (d%)
01-16: Dahak
17-32: Ghlaunder
33-49: Gyronna
50-70: Eldest, Ragadhan
71-99: Forgotten deity, Ydersius
00: Other
Other deity (NE, CN) (d%)
01-14: Besmara
15-28: Groetus
29-42: Hanspur
43-56: Zyphus
57-70: Eldest, Count Ranalc
71-84: Eldest, Green Mother
86-98: Eldest, Lantern King)
99-00: Other or reroll
Elemental lord (NE), Horseman (NE), or forgotten deity (CN) (d%)
01-12: Elemental lord, Ayrzul
13-24: Elemental lord, Hshurha
25-36: Elemental lord, Kelizandri
37-48: Elemental lord, Ymeri
49-54: Horseman, Apollyon
55-60: Horseman, Charon
61-66: Horseman, Szuriel
67-72: Horseman, Trelmarixian
73-00: Forgotten deity, Great Old Ones (CN)
Other deity (LE, N, CG) (d%)
01-33: Achaekek (LE)
34-66: Sivanah (N)
67-99: Milani (CG)
00: Other or reroll
Archdevils (LE) (d%)
01-12: Baalzebul
13-24: Barbatos
25-36: Belial
37-48: Dispater
49-60: Geryon
61-72: Mammon
73-84: Mephistopheles
84-96: Moloch
97-00: reroll
Eldest, Empyreal lord, forgotten deity (LE, N, CG) (d%)
01-13: Eldest, Lost Prince (N)
14-26: Eldest, Ng (N)
27-39: Eldest, Shyka (N)
40-59: Empyreal lord, Sinashakti (CG)
60-79: Empyreal lord, Valani (CG)
80-00: Forgotten deity, Lissala (LE)
Other deity, Eldest, Empyreal Lord (LN, NG) (d%)
01-15: Other deity, Kurgess (NG)
16-32: Eldest, Imbrex (LN)
33-49: Eldest, Magdh (LN)
50-75: Empyreal Lord, Arshea (NG)
76-00: Empyreal Lord, Korada (NG)
Other deity, Empyreal lord (LG) (d%)
01-34: Other deity, Apsu
35-67: Empyreal lord, Andoletta
68-00: Empyreal lord, Ragathiel