Eclectic solitary Wicca has no founder, no founding date and no organisation, and any account that supplies one is wrong. It is what happened when a religion transmitted by initiation met a mass paperback market.
The practitioner works alone, assembles a practice from published sources, and typically marks the beginning of it with a self-dedication rather than an initiation conferred by anyone else. There is no coven, no oath, no lineage, and nobody to ask. There is also, by construction, no orthodoxy: an eclectic practice may draw on Gardnerian ritual structure, on Celtic or Norse or Egyptian names, on ceremonial magic, herbalism, tarot, and whatever else the practitioner finds it useful to work with.
This is now, by a very large margin, the way most self-identified Wiccans practise. It is what the word means to most of the people who use it about themselves.
The published self-initiation rite goes back to Paul Huson's Mastering Witchcraft of 1970, and Doreen Valiente and others followed. The book that made the category is Scott Cunningham's Wicca: A Guide for the Solitary Practitioner, published in 1988, which had sold over four hundred thousand copies by 2000 and told its reader, in plain language, that they could simply begin. Silver RavenWolf and a long line of others followed the model, and the internet, from the mid-1990s, removed the last barrier to entry.
None of this was planned by anyone, and no initiatory body authorised it. It happened because demand exceeded the supply of initiators by several orders of magnitude, and a printing press was available.