Sergei Tarsian

Affiliation: Ishida Finance

A friend of Karin's, Tarsian seems to have a connection to Karin's parents, and doesn't talk during instant message conversations.

[Spoiler] Tarsian makes a physical appearance from halfway through the series. He is chairman of Atlas Corporation, and apparently knows Ryoko well. It is revealed that Tarsian and Nagiko, the first CEO of Atlas, both helped create Atlas for a better future for their descendants. He is placed under arrest by Ryoko under allegations of having assisted an unknowing Karin to shut down Atlas' critical systems. [/Spoiler]

(Source: Wikipedia)