Alfonso Calderón Atienzar is a Spanish-American student activist against gun violence. He is a survivor of the Stoneman Douglas High School shooting and a founding member of the Never Again MSD movement.

Never Again MSD is an American student-led political action committee for gun control that advocates for tighter regulations to prevent gun violence. The organization, also known by the Twitter hashtags #NeverAgain, and #EnoughIsEnough, was formed by a group of twenty students attending Marjory Stoneman Douglas High School (MSD) at the time of the deadly shooting in 2018, in which seventeen students and staff members were killed by the alleged gunman, Nikolas Cruz, who was a 19-year-old former student of the school and was armed with an AR-15 style semi-automatic rifle. The organization started on social media as a movement "for survivors of the Stoneman Douglas Shooting, by survivors of the Stoneman Douglas Shooting" using the hashtag #NeverAgain. A main goal of the group was to influence that year's United States mid-term elections, and they embarked on a multi-city bus tour to encourage young people to register to vote.