Atomwaffen Division
Atomwaffen Division ("Atomic weapons division") is a group stated to be influenced by the principle of "leaderless resistance", James Mason, occultism/Satanism, and other influences. As such, it presumably does not have a central leadership, but instead consists of a network of loosely associated but independent groups and individuals.
Individuals/groups in the network have been stated to have been inspired by/idolized criminals such as Charles Manson, Anders Breivik, and Dylann Roof. Several associated individuals have been convicted or accused of various crimes. One example is two stated murders of Atomwaffen Division members by another Atomwaffen Division member who had been ridiculed for converting to Islam.
For example the leftist Wikipedia associate these crimes with the Alt-Right and pro-White organizations in general which is guilt by association. In other cases, such regarding the large-scale existence of Islamist terrorists organizations and networks, all pro-Islam groups are not similarly accused by Wikipedia by using guilt by association.
Various claims regarding size and influence may be dubious, as both supporters and some critics may have an interest in inflating this.
