Aimee Elizabeth Semple McPherson (ne Kennedy; October 9, 1890 September 27, 1944), also known as Sister Aimee or Sister, was a Canadian Pentecostal evangelist and media celebrity in the 1920s and 1930s, famous for founding the Foursquare Church. McPherson pioneered the use of broadcast mass media for wider dissemination of both religious services and appeals for donations, using radio to draw in both additional audience and revenue with the growing appeal of popular entertainment and incorporating stage techniques into her weekly sermons at Angelus Temple, an early megachurch.In her time, she was the most publicized Protestant evangelist, surpassing Billy Sunday and other predecessors. She conducted public faith healing demonstrations involving tens of thousands of participants. McPherson's view of the United States as a nation founded and sustained by divine inspiration influenced later pastors.

National news coverage focused on events surrounding her family and church members, including accusations she fabricated her reported kidnapping. McPherson's preaching style, extensive charity work and ecumenical contributions were a major influence on 20th century Charismatic Christianity.

In Christianity, evangelism (or witnessing) is the act of preaching the gospel with the intention of sharing the message and teachings of Jesus Christ.

Christians who specialize in evangelism are often known as evangelists, whether they are in their home communities or living as missionaries in the field, although some Christian traditions refer to such people as missionaries in either case. Some Christian traditions consider evangelists to be in a leadership position; they may be found preaching to large meetings or in governance roles. In addition, Christian groups who encourage evangelism are sometimes known as evangelistic or evangelist.