In the true-est sense, a classic Evangelist is one who "markets" or promotes their faith ie: tv evangelists - lets people know about it...
however in recent technological terms - ie:
Technology Evangelist, Apple Evangelist, SEO evangelist etc. the term has been adopted to promote support for a given technology in order to get establishment in the marketplace
Evangelism is the Christian practice of preaching the Gospel of Jesus to both Christians (i.e. Orthodox and Catholics) or non-Christians. The intention of most evangelism is to effect conversion to Christianity. Evangelism is done in obedience to the Great Commission; instruction from Jesus to his disciples to proselytise, as recorded in the New Testament. Christians who specialize in evangelism are known as evangelists, whether in their home communities or as missionaries. Some Christian traditions consider evangelists to be in a leadership position, and they may be found preaching to large meetings, and in governance roles.
It would range from Zero for a Jehovah's Witnesses evangelist; to an enormously high number for a Protestant evangelist.
The noun evangelist has the regular S plural evangelists.
Francis Murphy - evangelist - died in 1907.
John Darby - evangelist - was born in 1800.
Henry Drummond - evangelist - died in 1897.
Johann Evangelist Holzer was born in 1709.
Johann Evangelist Holzer died in 1740.
John Evangelist Stadler was born in 1804.
John Evangelist Stadler died in 1868.
David Watson - evangelist - was born in 1933.
Francis Murphy - evangelist - was born in 1836.
Paul Rader - evangelist - died in 1938.