Kirk, a devout Christian, was a strong supporter of gun rights, vehemently opposed abortion, was critical of transgender and gay rights, and promoted false claims about Covid-19.
His supporters said he was relatable, understood their concerns and was able to hold respectful debates with those he disagreed with.
But his views drew fierce liberal criticism, with his detractors calling his comments deeply offensive to some minority groups, including LGBT people and Muslims.
Turning Point USA, which Kirk co-founded, aimed to spread conservative ideals at liberal-leaning US colleges, and played a key role in getting people to vote for Trump and other Republican candidates in the election last year.