John Carmack, the CTO of Oculus, has sued his former employer, ZeniMax Media, for alleged breach of contract.

In the lawsuit, which was filed on Tuesday, Carmack claims that he is owed over $22.5 million as part of the 2009 deal in which ZeniMax Media bought id Software. Carmack co-founded id Software in 1991, which created Wolfenstein, Doom, Quake, and a number of other legendary video game titles. He left id Software in 2013 and quickly joined Oculus.

Carmack, Oculus, and ZeniMax Media have been entangled in an ongoing legal battle for years over questions surrounding the development of the Oculus VR headset. ZeniMax sued Oculus in 2014 over misappropriation of trade secrets, copyright infringement, and breach of contract, among other accusations. The civil lawsuit went to trial earlier this year and resulted in a jury finding that Oculus was liable for $300 million. Carmack, who was accused of stealing code and destroying evidence, was found not to be personally liable for any damages. ZeniMax had sought damages of $6 billion in the case. Oculus, which vowed to appeal, has not done so yet.

The new civil case says that ZeniMax agreed to pay $150 million, in installments, to acquire id Software.

"Now that the final installment of that bill is coming due, ZeniMax is simply refusing to pay," Carmack's lawyers argue in the complaint. "But sour grapes is not an affirmative defense to breach of contract. This Court should enter judgment against ZeniMax for all the money that it agreed to pay Mr. Carmack for the sale of his former company."

ZeniMax did not respond to Ars' request for comment, but the Dallas Morning News published a statement Thursday from an unnamed spokeswoman who said that Carmack's claims were "completely without merit."

"Apparently lacking in remorse, and disregarding the evidence of his many faithless acts and violations of law, Mr. Carmack has decided to try again," the statement continued.