Mormon leader Boyd K. Packer, president of the faith's highest governing body, has died. He was 90.

Packer died Friday afternoon at his home in Salt Lake City from natural causes, church spokesman Eric Hawkins said in a statement. He was next in line to become president of the Salt Lake City-based Church of Jesus Christ of Latter-day Saints.

Packer was known for being a staunch advocate for a conservative form of Mormonism, making him an idol for like-minded, devout Latter-day Saints but also a target of frequent criticism from gay rights groups and more liberal Mormons.

He had been a member of the church's Quorum of the Twelve Apostles since 1970. The group is modeled after Jesus Christ's apostles and serves under the church president and his two counselors.

He is the second member of quorum to die in recent months. L. Tom Perry died on May 30 from cancer.

Quorum member Russell M. Nelson, 90, now becomes the leader who would take Mormon President Thomas S. Monson's place because he is now the most tenured of the group. Monson is 87 years old, and church officials have said he's feeling the effects of his age.

Replacements for Packer and Perry will be chosen sometime in the coming months by Monson, considered the religion's prophet. Members of the faith believe those decisions are guided by inspiration from God. Some past quorum members have been moved up from another governing body, the Quorum of the Seventy, while others have come from leadership posts at church-run universities.

When Packer was chosen for the group, he was already working for the church.

Packer was born Sept. 10, 1924 in Brigham City, Utah, and was a bomber pilot during World War II. He earned an undergraduate degree from Utah State University and a master's in educational administration from Brigham Young University.

During his 45 years as a member of the quorum, Packer became known as a fearless defender of the gospel and master teacher of church principles, the church said in a news release.

Utah Gov. Gary Herbert said in a statement that Packer was "unwavering in his devotion to his faith and the principles by which he lived his life." Herbert added that Packer's "strength and love were felt by church members throughout the world."

Fellow church leaders called him a true apostle for the religion.

"From the crown of his head to the soles of his feet, he represented the savior of the world," said quorum member M. Russell Ballard in a news release.

Packer spent most of his adult life working for the church and earned a reputation of being a tenacious advocate for his orthodox views on Mormonism, said Patrick Mason, chairman of the religion department and professor of Mormon studies at Claremont Graduate University in California. Some called him a bulldog, but Packer preferred the biblical analogy of "watchman on the tower," Mason said.

He was known for having a major influence within the church hierarchy and bureaucracy, having mentored at least one if not two generations of church leaders and bureaucrats, Mason said.

Packer is remembered for giving a speech in 1993 in which he warned that the religion faced the greatest threat from three groups: feminists, homosexuals and intellectuals.

In 2010, he denounced homosexual attraction as unnatural and immoral. His hostility toward homosexuality made him a target in recent years of gay rights advocates, said Armand Mauss, a Mormon scholar and retired professor of sociology and religious studies at Washington State University.

In 2013, a Utah gay-rights organization started a petition to protest the naming of a new Weber State University center after Packer.

Mauss said Packer will be remembered "for an unyielding resistance to the secular, social world, especially as that world evolved during his lifetime."

The church credits Packer with being a key driver of the religion's growth into a worldwide religion that now counts 15 million members around the globe.

He painted as a hobby, with birds being one of his favorite subjects. Packer was married to his wife, Donna, for more than 70 years. They had 10 children.

In one of his last speeches, during a church conference in April, Packer spoke about the joy of romance and love and the importance of a man and woman and their children being sealed in a Mormon temple for eternity. Packer acknowledged marriage is a challenge and offered the key ingredients to successful marriages: "a cookie and a kiss."

Funeral services have not yet been scheduled.