Were the Early Adventists Arians?

Arianism was a teaching about Jesus that arose in the fourth century. Though rejected at the Council of Nicaea in 325, it was fought over for another half century after that as succeeding emperors enforced Arianism or Trinitarianism as the official view of the church.

The basic teaching of Arius was "that the Son of God was not eternal but created by the Father from nothing as an instrument for the creation of the world; and that therefore He was not God by nature, but a changeable [mortal] creature, His dignity as Son of God having been bestowed on Him by the Father on account of His foreseen abiding righteousness" (Oxford Dictionary of the Christian Church, article "Arianism"). The Adventist pioneers have sometimes been called "semi-Arian" rather than Arian, because while they believed that Jesus had a beginning, they differed somewhat from the second part of the Arian definition. The Adventists believed that Christ did indeed partake of God's own nature and thus was not "merely" a creature, even though they held that at some time in distant eternity past God the Father had brought Him into existence.

Both the Arian and semi-Arian positions, however, were decisively refuted by Ellen White in Desire of Ages. (cf pp. 530, 785; see also E. G. White Comments, SDA Bible Commentary, 5:1113.)