Janus
Bill Gross
He is seeking "hundreds of millions of dollars", according to a report by Nathaniel Popper at The New York Times.
A complaint filed by Gross' lawyers alleges that "a cabal" of managing directors at PIMCO pushed him out as a result of "a lust for power, greed, and a desire to improve their own financial position", according to the report.
PIMCO is a fund behemoth with a whopping $1.52 trillion in assets under management as of June 30 2015.
The firm was at the center of one of the stories of 2014.
Then-CEO Mohamed El-Erian shocked the world with his surprise resignation in January 2014. That was quickly followed by a series of stories from The Wall Street Journal and Reuters about the unorthodox management style of founder and then-co-CIO Gross.
And after about nine months of drama, Gross rocked the finance industry with his own resignation announcement in September. Gross left the firm for Janus Capital, in a move that preempted his own firing.
PIMCO chief executive Douglas Hodge said at the time of Gross' departure that Gross and the firm's leaderhip had "fundamental differences."
The statement read: "While we are grateful for everything Bill contributed to building our firm and delivering value to PIMCO's clients, over the course of this year it became increasingly clear that the firm's leadership and Bill have fundamental differences about how to take PIMCO forward."
PIMCO declined to comment on Thursday when contacted by Business Insider.