The conservative activist known as Joe the Plumber is airing a TV ad in Missouri calling Rep. Roy Blunt (Mo.) a "pretender" and touting state Sen. Chuck Purgason as the best candidate for the Republican Senate nomination.

Samuel "Joe" Wurzelbacher said he purchased the statewide ad time without Purgason's knowledge and filed appropriate paperwork with the Federal Election Commission, according to the St. Louis Post-Dispatch. The ad was originally a YouTube video.

Purgason's campaign hasn't raised enough cash to air its own TV ads.

"I wanted to show that individuals can have some say in what's going on," Wurzelbacher told the Post-Dispatch. "I called and got a couple of people to donate."

The fairytale-themed ad refers to Blunt as a "pretender to the conservative throne."

Wurzelbacher endorsed Purgason earlier this month. Since the 2008 presidential campaign, he has stayed in the political spotlight, criticizing the Obama administration and endorsing conservative candidates in various races. He has also appeared at several Tea Party rallies.

Purgason has billed himself as the "only true conservative" in the GOP primary against Blunt. But the congressman holds a commanding lead — 62 percent to 13 — over his rival, according to a recent Post-Dispatch poll. He's also outraised him by a ratio of nearly 300 to 1.

The winner of the Aug. 3 primary is expected to face Missouri Secretary of State Robin Carnahan (D) in November.