Since you asked ... Here's the background / context ...
During the two decades during which this forum (originally the Fortean Times Message Board) has been operating both the population of participating members and the underlying software platforms have changed.
I mention both these histories because the manner in which deleted / departed members' records were treated depended on which version of which software platform was being used - both at the time the member account was shut down and during transitions between different forum software platforms.
There's no straightforward way to assess this, but I'm pretty confident the single username credited with the most posts ever may well be "Anonymous" rather than rynner2. Anonymous is the default username attributed to member accounts which are missing, damaged to the point of being unrecognizable, or deleted.
After our most recent and most radical such transition (the Great Exodus of Autumn 2018) the cumulative member database resembled a hoarder's back room packed with decades' worth of junk - most of which was useless / unusable and much of which was a tangled mess.
Owing to the recently-imposed GDPR regulations and other issues we can not simply maintain pre-2018-migration members in perpetuity unless they have surfaced and acknowledged our new Terms & Conditions. It's now been 1.25 years since the migration.
As Yith mentioned, there's been a major housekeeping campaign in process for months now, aimed at:
(a) clearing out / reorganizing / cleaning up two decades' worth of carnage within the forum's contents and ...
(b) purging the member rolls of member accounts which aren't demonstrably "within bounds" with respect to T&C and other factors for which we are now legally responsible.
Much of the forum's most interesting and thoughtful content resides in the back corners (threads dating back to much earlier years). One problem with this material is that some discussions are dominated by the single username "Anonymous", which actually denotes multiple members who've come and gone.
In conducting the current massive housekeeping operation, we have been trying to avoid adding to Anonymous' bulk in terms of posts, number of past members subsumed within the single label, and the confusion it causes readers.
By the same token, we are revising all surviving dormant / obsolete member records so as to be (a) readily recognizable as dormant / obsolete yet (b) locked down to prevent problems relating to legalities and security.
As a result of all this, a new category of membership record has been established to contain dormant / obsolete records under their respective original usernames.
This is being done solely for past members who ever posted anything to the forum. This population of departed posters includes members whose post totals range into the thousands - e.g., the one with the highest post total to date (i.e., rynner2).
This approach avoids these past members' contributions being relegated to the already over-stuffed "Anonymous" attribution, and it affords readers the ability to tell who posted what.
It also affords the staff the ability to segregate such accounts and lock them down permanently to ensure they cannot be subverted or exploited as time goes on.
All such accounts are now flagged with a user banner entitled "Account Retired" to cue readers they're closed down and the associated person has probably been gone for a long time now.
Costly and awkward. Renaming them all to Anonymous, then freezing them, is surely a lot more practical.
The question then simply becomes one of storage (I'd suggest classic horizontal, as opposed to upright.....we'd never see over the heads of tall ones that'd get stacked at the front. Plus they'd topple.
And I hope we all take our fair turn on that forklift, just because I'm fast with it doesn't mean I want to be left using the damn thing all night).
Not really ... The additional storage burden for maintaining separate batches of basic member data for each preserved account is comparatively insignificant.
The storage burden for maintaining the internal indices and links for all the thousands of associated posts is essentially the same one way or the other. All that bookkeeping still has to be done whether the contributions map to one catch-all "Anonymous" or all the actual members who generated them.
In any case, it's more than counterbalanced by the storage savings obtained by eliminating old un-migrated / unused / abandoned accounts associated with members who never participated (posted anything) at all - some of whom hadn't visited since 2001.
Which in turn leads me to the following ...
Forum Fun Fact (that I'm both surprised and disappointed no one's noticed / noted over the last few months ... )
On the forum's main / top-level entry page there's a segment labeled "Forum Demographics."
One of the items listed there is the number of Members.
On the first anniversary of our being notified the FTMB was to be destroyed that number stood at something over 35,000.