Pierpont

Pierpont is a Sapphire Archon. He was likely a mentor to Rylai. Mireska has heard of Pierpont, and Donte Panlin seems to know him personally.

Speculation
It is possible that Pierpont is the same person as the unnamed Ice Wizard who mentored Rylai, although this is unconfirmed.

Trivia

 * Pierpont is based on a concept by Drew Wolf, a former Valve design artist.