No, he isn’t. His weird politics is explained by radlib free speech brainworms, which you would expect from someone running a project like Wikileaks. I suppose technically Wikileaks could be used by the US or other government selectively leaking to them, but in the case of the US anything they want leaked they can just give to a totally compliant media anyway, so I don’t think this has ever been the case (possibly Russia did selectively leak Clintons emails to WL though).
The media payed attention to WL’s stories - when they were leaking major shit they were getting more website hits than major media organisations anyway, so the MSM had no choice but to pay attention.
US intelligence made plans to assassinate Assange, there is no plausible way he is an asset.