LONDON, May 20 (Reuters) - An Australian computer scientist who claimed he invented bitcoin lied "extensively and repeatedly" and forged documents "on a grand scale" to support his false claim, a judge at London's High Court ruled on Monday.

Craig Wright had long claimed to have been the author of a 2008 white paper, the foundational text of bitcoin, published under the pseudonym "Satoshi Nakamoto".

But Judge James Mellor ruled in March that the evidence Wright was not Satoshi was "overwhelming", after a trial in a case brought by the Crypto Open Patent Alliance (COPA) to stop Wright suing bitcoin developers.

Mellor gave reasons for his conclusions on Monday, stating in a written ruling: "Dr Wright presents himself as an extremely clever person. However, in my judgment, he is not nearly as clever as he thinks he is."

The judge added: "All his lies and forged documents were in support of his biggest lie: his claim to be Satoshi Nakamoto."

Mellor also said that Wright's actions in suing developers and his expressed views about bitcoin also pointed against him being Satoshi.

Wright, who denied forging documents when he gave evidence in February, said in a post on X: "I fully intend to appeal the decision of the court on the matter of the identity issue."

COPA – whose members include Twitter founder Jack Dorsey's payments firm Block – described Monday's ruling as "a watershed moment for the open-source community".

"Developers can now continue their important work maintaining, iterating on, and improving the bitcoin network without risking their personal livelihoods or fearing costly and time-consuming litigation from Craig Wright," a COPA spokesperson said.

(Reporting by Sam Tobin; Editing by Emelia Sithole-Matarise)