Octans is an agent of the Collective who works at the Collective Base. Found in the base's personnel quarters, the Charlatan entrusts him with mentoring new recruits.
Should Pathfinder Ryder help investigate who's faking the Charlatan's orders, Octans emerges as one of five suspects despite being a salarian and not matching the criterion of having humanoid footprints. He does have high levels of sulfur (the other criterion), prompting SAM to note in his analysis that Octans could use a bath.
When one of the recruits ask when he's going to meet the Charlatan, Octans laughs and informs him few people ever do. He himself hasn't met the Collective leader. He knows Meriweather and maybe Crux has, though it isn't information that's freely shared.