Most of us have spoken to one. Some may have even been in your house. Volunteer campaigners are the lifeblood of political parties.
They knock on doors, deliver leaflets and man phones - getting the message out for their chosen party.
In the age of social media the 'air war' - the battle between politicians in the news - is being fought like never before, but parties still rely on this army of helpers.
We spoke to some of them about how campaigning has changed and why someone would give up their free time for a political party.
Sandy Cowling, 72, Labour
"I met my husband at a Labour meeting," she said.
"When we began our relationship I knew there wasn't a lot that could go wrong because we'd been leafleting together.
"I've always been a fairly outgoing person - my family would say I have far too many opinions, so it's quite nice to share one's opinions and talk to people who are like-minded.
"The most successful people, regardless of social media and what's changed, are the people who are known and seen.
"It shouldn't be: 'Oh you've turned up now.' It should be: 'Oh god, it's you again.'
"I've had some great experiences and met some wonderful people and at least if the wrong side get in, it wasn't my fault."
Jack McAteer, 19, Liberal Democrats
"During the long summer months at the end of the school year I decided I had to stop moaning and get involved," Jack said.
"I was raised in a political household and I have always had the confidence to say this is wrong.
"At first, when I knocked on this door, I had to have a friend with me because it was quite scary but I enjoy it now.
"It felt incredibly patronising. Older generations think I've been here for five minutes and now I'm telling them what to do - but what is the alternative?
"It's a good feeling getting out there to change things."
Hannah Angel, 22, Conservatives
"Campaigning has changed my life," she says. "I used to be quite shy at school and college.
"Going out, meeting new people, learning about new areas is now fascinating to me.
"The passion for getting your party elected overcomes any anxiety about knocking on doors. The more you do it the more your confidence builds up.
"Campaigning is very rewarding and I believe everyone who has an interest in politics should do it at one point in their life.
"It's humbling in a way to know there is a different perspective, but it's also made me feel firmer in my own beliefs."
Andrew McCarthy, 66, Conservatives
"Politics is becoming increasingly distant from the citizens. Focussing instead on the so called 'air war' - what happens on TV and online - and I don't like that.
"Being on receive rather than transmit, and talking to people on the doorstep is really important.
"It's a wonderful reflection of our democracy that so many people will come out to talk to you. In a lot of countries they'd think you'd come round to shoot then.
"There's a lot of good camaraderie - you're out with your friends. I have been spat at, but it's pretty rare.
Muhammed Ravat, 24, Labour activist
"I started working as an imam around the start of Sadiq Khan's selection as Labour's mayoral candidate.
"I was just fresh out of training and the possibility of having a Muslim mayor in London was fantastic - it helped inspire me.
"I got engaged and I realised there was a way of helping people and public service through politics.
"For this election I've done 135 sessions so far. I get a real buzz out of it.
"I specifically enjoy going to marginal boroughs, where every consultation could be the difference. We need as many councillors as we can.