"I remember driving in his old, second-hand Nissan Patrol," Joyce says.

"I thought, 'this is just what we need in politics. Someone who has a real understanding of the world the voters live in'."

Williams had been a shearer, truck driver, farmer and small business owner before he took on sitting member Sandy Macdonald to win preselection for the Nationals in 2007. He'd been a member of the party since the 1980s, but when he came to Canberra, made it clear to then-leader Warren Truss he had no desire for frontbench promotions.

"I just wanted to be me."

True to his word, during his eleven-year career in the Senate, Williams' name has never been suggested as a frontbench contender, despite the innumerable reshuffles in that time. His most senior parliamentary position has been as Nationals whip in the Senate.

But as Joyce (who sensationally quit the Nationals leadership last year) notes, "you can be a minister and a nobody really easily. Getting yourself on to the blue carpet [of the ministerial wing] does not mean you've had great political success".

On Wednesday, Williams will give his final speech to Parliament, before his retirement on July 1. The timing of the 64-year-old's departure is poetic. As one of the driving forces for a royal commission into banking, the Nationals senator leaves just as Commissioner Kenneth Hayne's final report sends shockwaves through the financial sector.

In a sign of the impact the NSW backbencher has had, Commonwealth Bank chief executive officer Matt Comyn will be in the public gallery to see Williams' valedictory, along with his children, grandchildren and good friend Kamahl.

Williams, who lost his family farm in the 1980s after dud financial advice from the Commonwealth Bank, was the first parliamentary voice to call for a royal commission - years before the Coalition or Labor supported the idea. While he says he didn't enter Parliament to take on the banks, seven months into his first term, he was deeply affected by meeting a group of retirees who had lost their savings in the Storm Financial collapse.

"It was just something I couldn't take," he says. "Life's about fairness."

Greens senator Peter Whish-Wilson, a former Wall Street banker, has worked alongside Williams on Senate inquiries into the financial sector for more than five years. Whish-Wilson had not been in Canberra long - and didn't even know who "Wacka" was - when Williams bailed him up in a parliamentary corridor and insisted he join an inquiry that would ultimately back a royal commission in 2014.

(The nickname "Wacka" was earned as a young child, when he would do nude runs after bath time and his father would say, "Wacko!".)

"He said, 'I know you've got a background in banking. We're going after ASIC'," Whish-Wilson says.

Whish-Wilson says the moment has stuck with him because it is unusual for colleagues in Canberra to want you involved if they think you're an expert lest you show them up. But Whish-Wilson says Williams was always more interested in the actual issues, than squabbling over territory.

"I always trusted him," the Tasmanian Greens senator says.

Williams' crusade against the banks has been long and often lonely. In Parliament, it has meant doing unpopular things like crossing the floor to vote with the Greens. Tellingly, it was Williams who finally took Commonwealth Bank whistleblower Jeff Morris seriously, when the former financial planner got in touch looking for action in 2013.

While the royal commission is his headline achievement, Williams says his real victories have happened behind closed doors - mediating between victims and the banks. For years, the NSW senator has also been inundated with calls from victims of bad advice, looking for help.

Beyond the financial sector, Williams interests have ranged far and wide. He has also been an advocate for country of origin labelling for food and speed limits for mobility scooters after his wife was hit and injured by a speeding "gopher".

A devout Catholic, Williams was one of 12 senators to vote against same-sex marriage in in 2017. He was also one of the key voices to shoot down Tony Abbott's "signature" paid parental leave scheme after the 2013 election, threatening to cross the floor to defeat it.

Since 2010, the NSW senator has sponsored a $4800 dental scholarship for regional students, based on funds from an electoral allowance increase given to all MPs.

But Williams has also become involved in issues that are not so close to his heart. Whish-Wilson remembers Williams once drive nine hours in a day to get to Byron Bay to make sure the Greens senator's committee had a quorum, so a hearing into shark protection could go ahead.

Williams consequently "copped it from greenies all day".

"He did it for me. He knew the issue was important to me," says Whish-Wilson.

Labor's Deborah O'Neill, who has sat on the Corporations and Financial Services Committee with Williams for seven years, says she will miss Williams' "colourful turn of phrase," which cuts through "pomposity" in the political world.

O'Neill points to a recent committee hearing into the franchising code of conduct, when Williams was questioning former Retail Food Group executives about events leading up to a $427 million write-down in assets.

It's not often that "tits up" appears in the parliamentary Hansard.

Williams laments that all most voters see of politics is TV grabs of MPs throwing "hand grenades" at each other, when often, behind-the-scenes, people are working hard at working together. As Nationals whip he insisted the party's senators meet every Wednesday afternoon for tea and lamingtons. He has maintained the same four full-time staff in his Inverell office during his entire time in politics.

Last week, Williams was talking to his wife Nancy about life after politics. Over a beer at their farm in Inverell, she asked him, "come July 1, how are you going to feel about being Citizen Wacka instead of Senator Wacka?".

Thinking it over, Williams insists he will just be grateful for the opportunity. "I'm not going to weep and wail in sympathy for myself," adding there is plenty on his retirement bucket list.

The fence needs fixing on his farm and there is an ongoing battle to be fought against weeds.

He wants to ride in a Lancaster Bomber, in honour of his father, Reg, who was a rear gunner during World War II. He also plans to travel with Nancy to Canada, the United States, Ireland and France, in search of bush, battlefields and family history.

If he can, he also wants to help Parkinson's Australia. In 2017, Williams revealed he was suffering from the disease, but says he can report good news. A recent consultation with his neurologist revealed the disease is progressing very slowly.

"I've drawn the lucky card."