Here are the major visual references for the development of Aeligos. Both Tsar Project and Qasir al-Wasat draw much from Goetian occultism [fig. 1]. Aeligos is himself a Goetian Demon and there are many previous representations of him, those were used more as reference then inspiration, since we wanted to depart from the obvious with our Southerns.
Nevertheless Aeligos should still be defined as a knight, and thus one of the main elements was his armor [fig. 2]. I picked the late gothic style for it fitted Tsar Project both chronologically and aesthetically. The sallet helmet is both underused and uncomfortably evil, so that was a no-brainer choice.
Traditionally Aeligos is depicted mounting a dragon, but since dragons and snakes are usually akin I went with the huge constrictor [fig. 3]. From this the idea that he could be both the python and the armor quickly developed.
Lastly there is the wonderful work of Yoji Shinkawa [fig. 4] — art director for most of Hideo Kojima’s work — that was used as stylistic compass for all the Outplannars, both Southerners and Northerners.