diff --git a/Bugzilla/DB/Schema.pm b/Bugzilla/DB/Schema.pm
index a2bbd3224a..f264849a58 100644
--- a/Bugzilla/DB/Schema.pm
+++ b/Bugzilla/DB/Schema.pm
@@ -747,6 +747,12 @@ use constant ABSTRACT_SCHEMA => {
         NOTNULL    => 1,
         REFERENCES => {TABLE => 'profiles', COLUMN => 'userid'},
       },
+      # The user who made the change. Not always the setter: redirecting a
+      # request keeps the original setter. Nullable until all pods write it.
+      who          => {
+        TYPE       => 'INT3',
+        REFERENCES => {TABLE => 'profiles', COLUMN => 'userid'},
+      },
       requestee_id => {
         TYPE       => 'INT3',
         REFERENCES => {TABLE => 'profiles', COLUMN => 'userid'},
@@ -767,6 +773,7 @@ use constant ABSTRACT_SCHEMA => {
       flag_activity_type_id_idx     => ['type_id'],
       flag_activity_bug_id_idx      => ['bug_id'],
       flag_activity_status_when_idx => ['status', 'flag_when'],
+      flag_activity_who_idx         => ['who', 'flag_when'],
     ],
   },
 
diff --git a/Bugzilla/Flag.pm b/Bugzilla/Flag.pm
index f582bfcaa0..7779512597 100644
--- a/Bugzilla/Flag.pm
+++ b/Bugzilla/Flag.pm
@@ -491,6 +491,7 @@ sub create {
   Bugzilla::FlagActivity->create({
     flag_when     => $timestamp,
     setter_id     => $flag->setter_id,
+    who           => Bugzilla->user->id || $flag->setter_id,
     status        => $flag->status,
     type_id       => $flag->type_id,
     flag_id       => $flag->id,
@@ -519,6 +520,7 @@ sub update {
     Bugzilla::FlagActivity->create({
       flag_when     => $timestamp,
       setter_id     => $self->setter_id,
+      who           => Bugzilla->user->id || $self->setter_id,
       status        => $self->status,
       type_id       => $self->type_id,
       flag_id       => $self->id,
@@ -595,6 +597,7 @@ sub update_flags {
     Bugzilla::FlagActivity->create({
       flag_when     => $timestamp,
       setter_id     => Bugzilla->user->id || $old_flag->setter_id,
+      who           => Bugzilla->user->id || $old_flag->setter_id,
       status        => 'X',
       type_id       => $old_flag->type_id,
       flag_id       => $old_flag->id,
@@ -716,6 +719,7 @@ sub force_retarget {
       Bugzilla::FlagActivity->create({
         flag_when     => $timestamp,
         setter_id     => Bugzilla->user->id || $flag->setter_id,
+        who           => Bugzilla->user->id || $flag->setter_id,
         status        => 'X',
         type_id       => $flag->type_id,
         flag_id       => $flag->id,
diff --git a/Bugzilla/FlagActivity.pm b/Bugzilla/FlagActivity.pm
index da41a79980..4ed09aa76d 100644
--- a/Bugzilla/FlagActivity.pm
+++ b/Bugzilla/FlagActivity.pm
@@ -29,6 +29,7 @@ use constant DB_COLUMNS => qw(
   type_id
   flag_id
   setter_id
+  who
   requestee_id
   bug_id
   attachment_id
@@ -69,6 +70,7 @@ use constant VALIDATORS => {
   type_id   => _check_param_required('type_id'),
   flag_id   => _check_param_required('flag_id'),
   setter_id => _check_param_required('setter_id'),
+  who       => _check_param_required('who'),
   bug_id    => _check_param_required('bug_id'),
   status    => \&_check_status,
 };
@@ -77,6 +79,7 @@ sub flag_when     { return $_[0]->{flag_when} }
 sub type_id       { return $_[0]->{type_id} }
 sub flag_id       { return $_[0]->{flag_id} }
 sub setter_id     { return $_[0]->{setter_id} }
+sub who           { return $_[0]->{who} }
 sub bug_id        { return $_[0]->{bug_id} }
 sub requestee_id  { return $_[0]->{requestee_id} }
 sub attachment_id { return $_[0]->{attachment_id} }
diff --git a/Bugzilla/Install/DB.pm b/Bugzilla/Install/DB.pm
index 5147beaa07..dbda8e1faa 100644
--- a/Bugzilla/Install/DB.pm
+++ b/Bugzilla/Install/DB.pm
@@ -844,6 +844,10 @@ sub update_table_definitions {
   # Bug 1949556 - dkl@mozilla.com
   $dbh->bz_add_index('audit_log', 'audit_log_object_id_idx', ['object_id']);
 
+  # Bug 2088705 - xavier.lhour@gmail.com
+  # Before _migrate_flag_state_activity, which copies into this column.
+  _add_flag_activity_who();
+
   # Bug 1806896 - xavier.lhour@gmail.com
   _migrate_flag_state_activity();
 
@@ -4531,16 +4535,34 @@ sub _migrate_flag_state_activity {
   # id is not carried over: nothing references flag_activity.id externally.
   $dbh->do(
     'INSERT INTO flag_activity
-       (flag_when, type_id, flag_id, setter_id, requestee_id, bug_id,
+       (flag_when, type_id, flag_id, setter_id, who, requestee_id, bug_id,
         attachment_id, status)
-     SELECT flag_when, type_id, flag_id, setter_id, requestee_id, bug_id,
-            attachment_id, status
+     SELECT flag_when, type_id, flag_id, setter_id, setter_id, requestee_id,
+            bug_id, attachment_id, status
        FROM flag_state_activity'
   );
 
   $dbh->bz_drop_table('flag_state_activity');
 }
 
+# Nullable for now: during the rolling deploy, pods still on the previous code
+# insert rows without it. Bug 2085398 makes it NOT NULL once all pods write it.
+sub _add_flag_activity_who {
+  my $dbh = Bugzilla->dbh;
+
+  $dbh->bz_add_column('flag_activity', 'who',
+    {TYPE => 'INT3', REFERENCES => {TABLE => 'profiles', COLUMN => 'userid'}});
+
+  # For the user activity report and the changedby search.
+  $dbh->bz_add_index('flag_activity', 'flag_activity_who_idx',
+    [qw(who flag_when)]);
+
+  # Rows from before this column, or from pods on the previous code, don't
+  # record who made the change: the setter is the best value available. Runs
+  # every time, on the index above.
+  $dbh->do('UPDATE flag_activity SET who = setter_id WHERE who IS NULL');
+}
+
 sub _remove_duo_recovery_codes {
   my $dbh = Bugzilla->dbh;
 
diff --git a/scripts/remove-non-public-data.pl b/scripts/remove-non-public-data.pl
index c4cffc202a..29d9915387 100755
--- a/scripts/remove-non-public-data.pl
+++ b/scripts/remove-non-public-data.pl
@@ -94,7 +94,7 @@ BEGIN
   ],
   flag_activity => [
     qw(
-      id flag_when type_id flag_id setter_id requestee_id bug_id
+      id flag_when type_id flag_id setter_id who requestee_id bug_id
       attachment_id status
       )
   ],
@@ -268,6 +268,7 @@ BEGIN
            AND (SELECT COUNT(*) FROM flags WHERE flags.setter_id = profiles.userid) = 0
            AND (SELECT COUNT(*) FROM flags WHERE flags.requestee_id = profiles.userid) = 0
            AND (SELECT COUNT(*) FROM flag_activity WHERE flag_activity.setter_id = profiles.userid) = 0
+           AND (SELECT COUNT(*) FROM flag_activity WHERE flag_activity.who = profiles.userid) = 0
            AND (SELECT COUNT(*) FROM flag_activity WHERE flag_activity.requestee_id = profiles.userid) = 0
 ");
 
diff --git a/t/flag-activity-who.t b/t/flag-activity-who.t
new file mode 100644
index 0000000000..2dc6109712
--- /dev/null
+++ b/t/flag-activity-who.t
@@ -0,0 +1,96 @@
+#!/usr/bin/env perl
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+# This Source Code Form is "Incompatible With Secondary Licenses", as
+# defined by the Mozilla Public License, v. 2.0.
+use strict;
+use warnings;
+use 5.10.1;
+use lib qw( . lib local/lib/perl5 );
+
+BEGIN {
+  $ENV{LOG4PERL_CONFIG_FILE}     = 'log4perl-t.conf';
+  $ENV{BUGZILLA_DISABLE_HOSTAGE} = 1;
+}
+
+use Bugzilla::Test::MockLocalconfig (urlbase => 'http://bmo.test');
+use Bugzilla::Test::MockDB;
+use Bugzilla::Test::MockParams (mail_delivery_method => 'None');
+use Bugzilla::Test::Util qw(create_bug create_user);
+use Bugzilla::Bug;
+use Bugzilla::Install::DB;
+use Bugzilla::User;
+use Test2::V0;
+
+# Redirecting a request keeps the original setter, but flag_activity.who
+# records the user who redirected it. The column stays nullable while pods on
+# the previous code still insert rows without it.
+
+create_user('automation@bmo.tld', '*');
+Bugzilla->set_user(Bugzilla::User->super_user);
+my $dbh = Bugzilla->dbh;
+
+my $requester  = create_user('requester@bmo.test',  '*');
+my $redirector = create_user('redirector@bmo.test', '*');
+create_user($_, '*') for qw(bob@bmo.test carol@bmo.test);
+
+my $bug_id = create_bug(
+  short_desc  => 'Flag redirect test bug',
+  comment     => 'Bug for the flag_activity who tests',
+  bug_type    => 'defect',
+  assigned_to => 'nobody@mozilla.org',
+)->id;
+my ($needinfo_id)
+  = $dbh->selectrow_array("SELECT id FROM flagtypes WHERE name = 'needinfo'");
+
+Bugzilla->set_user($requester);
+my $bug = Bugzilla::Bug->new($bug_id);
+$bug->set_flags([],
+  [{type_id => $needinfo_id, status => '?', requestee => 'bob@bmo.test'}]);
+$bug->update('2026-01-01 10:00:00');
+
+Bugzilla->set_user($redirector);
+$bug = Bugzilla::Bug->new($bug_id);
+my ($flag) = @{$bug->flags};
+$bug->set_flags(
+  [{id => $flag->id, status => '?', requestee => 'carol@bmo.test'}], []);
+$bug->update('2026-01-01 11:00:00');
+
+$flag = Bugzilla::Flag->new($flag->id);
+is($flag->setter_id, $requester->id, 'the setter is kept on redirect');
+
+my $rows = $dbh->selectall_arrayref(
+  'SELECT setter_id, who FROM flag_activity WHERE flag_id = ? ORDER BY id',
+  {Slice => {}},
+  $flag->id
+);
+is(
+  $rows,
+  [
+    {setter_id => $requester->id, who => $requester->id},
+    {setter_id => $requester->id, who => $redirector->id},
+  ],
+  'who is the user who made each change'
+);
+
+# A pod on the previous code inserts a row without who: it's saved, and the
+# next checksetup fills it with the setter.
+$dbh->do(
+  'INSERT INTO flag_activity (flag_when, type_id, flag_id, setter_id, bug_id,
+                              status)
+   VALUES (?, ?, ?, ?, ?, ?)', undef, '2026-01-01 12:00:00', $needinfo_id,
+  $flag->id, $requester->id, $bug_id, 'X'
+);
+Bugzilla::Install::DB::_add_flag_activity_who();
+my ($who)
+  = $dbh->selectrow_array(
+  "SELECT who FROM flag_activity WHERE flag_id = ? AND status = 'X'",
+  undef, $flag->id);
+is($who, $requester->id,
+  'a row inserted without who gets the setter on the next checksetup');
+ok(!$dbh->bz_column_info('flag_activity', 'who')->{NOTNULL},
+  'the column stays nullable');
+
+done_testing;