The Yang Gang is a nickname for supporters of 2020 Democratic presidential candidate, Andrew Yang. While the exact origins of the term "Yang Gang" are uncertain, the words may have come from a tweet comparing the fanbase to "Bernie Bros". 
On November 6th, 2017, Andrew Yang launched his campaign to run for president of the United States in 2020. In early 2018, Andrew Yang's campaign released a video titled "Andrew Yang for President | Humanity First" where he reveals his support for a universal basic income. A month later on March 30th, 2018, the campaign video was submitted to 4chan's/pol/board with the hashtag "#yanggang and it quickly picked up speed.
Rise In Popularity
Part of Yang Gang's rise in popularity can be attributed to Andrew Yang's unconventional media strategy. On February 12, 2019 Yang appeared on Joe Rogan's podcast to discuss his trademark "Freedom Dividend" policy proposal. He spoke about the rise of automation and inevitable loss of jobs, suggesting that we should place a tax on tech companies that pays out $1,000 a month to all citizens over the age of 18. The allure of a universal basic income paid for by the ultra-rich began to spread to the far corners of the internet. Soon countless memes sprang into existence playing on Yang's $12,000 a year safety net.
Controversy and Response
Somehow Yang's message found its way to white nationalists and fringe right wing groups who've been able to cherry pick select statements to use in their agendas. However Yang has completely rejected support from anyone affiliated with any group that spreads hate, in an interview with the The Verge he said: 
I denounce and disavow hatred, bigotry, racism, white nationalism, anti-Semitism and the alt-right in all its many forms. Full stop. For anyone with this agenda, we do not want your support. We do not want your votes. You are not welcome in this campaign.
After Yang's deputy Chief of Staff Carly Reilly tweeted, "UBI (universal basic income) is feminist", she was promptly doxed by angry 4Channers and rumors began to circulate that her former employer, RadicalMedia, was secretly being paid by the campaign to infiltrate 4chan. The harassment has caused the Yang staff to up their security measures, including extensive training for online moderators.