diff --git a/models/issues/reaction.go b/models/issues/reaction.go
index 0043379d6d8..70e0d18ba9c 100644
--- a/models/issues/reaction.go
+++ b/models/issues/reaction.go
@@ -350,7 +350,7 @@ func (list ReactionList) GetFirstUsers() string {
 		if buffer.Len() > 0 {
 			buffer.WriteString(", ")
 		}
-		buffer.WriteString(reaction.User.Name)
+		buffer.WriteString(reaction.User.DisplayNameWithFullName())
 		if rem--; rem == 0 {
 			break
 		}
diff --git a/models/user/user.go b/models/user/user.go
index 0349a469f91..8ba76136005 100644
--- a/models/user/user.go
+++ b/models/user/user.go
@@ -465,6 +465,7 @@ func (u *User) EmailTo() string {
 }
 
 // TODO: DefaultShowFullName causes messy logic, there are already too many methods to display a user's "display name", need to refactor them
+// Search this TODO to see more details
 // * user.Name / user.FullName: directly used in templates
 // * user.DisplayName(): always show FullName if it's not empty, otherwise show Name
 // * user.GetDisplayName(): show FullName if it's not empty and DefaultShowFullName is set, otherwise show Name
@@ -491,6 +492,14 @@ func (u *User) GetDisplayName() string {
 	return u.Name
 }
 
+// DisplayNameWithFullName returns the username, full name is included if it is not empty
+func (u *User) DisplayNameWithFullName() string {
+	if fullName := strings.TrimSpace(u.FullName); fullName != "" {
+		return fmt.Sprintf("%s (%s)", u.Name, fullName)
+	}
+	return u.Name
+}
+
 // ShortName ellipses username to length (still used by many templates), it calls GetDisplayName and respects DEFAULT_SHOW_FULL_NAME
 func (u *User) ShortName(length int) string {
 	return util.EllipsisDisplayString(u.GetDisplayName(), length)
diff --git a/models/user/user_test.go b/models/user/user_test.go
index 50a2eb70b4e..17ba7c339f5 100644
--- a/models/user/user_test.go
+++ b/models/user/user_test.go
@@ -295,18 +295,13 @@ func TestNewGitSig(t *testing.T) {
 }
 
 func TestDisplayName(t *testing.T) {
-	users := make([]*user_model.User, 0, 20)
-	err := db.GetEngine(t.Context()).Find(&users)
-	assert.NoError(t, err)
+	u := &user_model.User{Name: "name"}
+	assert.Equal(t, "name", u.DisplayName())
+	assert.Equal(t, "name", u.DisplayNameWithFullName())
 
-	for _, user := range users {
-		displayName := user.DisplayName()
-		assert.Equal(t, strings.TrimSpace(displayName), displayName)
-		if len(strings.TrimSpace(user.FullName)) == 0 {
-			assert.Equal(t, user.Name, displayName)
-		}
-		assert.NotEmpty(t, strings.TrimSpace(displayName))
-	}
+	u = &user_model.User{Name: "name", FullName: "Full Name"}
+	assert.Equal(t, "Full Name", u.DisplayName())
+	assert.Equal(t, "name (Full Name)", u.DisplayNameWithFullName())
 }
 
 func TestCreateUserEmailAlreadyUsed(t *testing.T) {
diff --git a/services/issue/reaction_test.go b/services/issue/reaction_test.go
index 62bb9e691d0..7cf5d155461 100644
--- a/services/issue/reaction_test.go
+++ b/services/issue/reaction_test.go
@@ -101,7 +101,7 @@ func TestIssueReactionCount(t *testing.T) {
 	reactions := reactionsList.GroupByType()
 	assert.Len(t, reactions["heart"], 4)
 	assert.Equal(t, 2, reactions["heart"].GetMoreUserCount())
-	assert.Equal(t, user1.Name+", "+user2.Name, reactions["heart"].GetFirstUsers())
+	assert.Equal(t, "user1 (User One), user2 (< U<se>r Tw<o > ><)", reactions["heart"].GetFirstUsers())
 	assert.True(t, reactions["heart"].HasUser(1))
 	assert.False(t, reactions["heart"].HasUser(5))
 	assert.False(t, reactions["heart"].HasUser(0))
diff --git a/templates/mail/repo/issue/assigned.tmpl b/templates/mail/repo/issue/assigned.tmpl
index 950d7b5cc49..49ee871c925 100644
--- a/templates/mail/repo/issue/assigned.tmpl
+++ b/templates/mail/repo/issue/assigned.tmpl
@@ -9,9 +9,9 @@
 <body>
 	<p>
 		{{if .IsPull}}
-			{{.locale.Tr "mail.issue_assigned.pull" .Doer.Name $link $repo_url}}
+			{{.locale.Tr "mail.issue_assigned.pull" .Doer.DisplayNameWithFullName $link $repo_url}}
 		{{else}}
-			{{.locale.Tr "mail.issue_assigned.issue" .Doer.Name $link $repo_url}}
+			{{.locale.Tr "mail.issue_assigned.issue" .Doer.DisplayNameWithFullName $link $repo_url}}
 		{{end}}
 	</p>
 	{{if .CanReply}}<p>{{.locale.Tr "mail.reply_directly"}}.</p>{{end}}
diff --git a/templates/mail/repo/issue/default.tmpl b/templates/mail/repo/issue/default.tmpl
index 917740b83a7..b306868bca6 100644
--- a/templates/mail/repo/issue/default.tmpl
+++ b/templates/mail/repo/issue/default.tmpl
@@ -17,34 +17,34 @@
 				{{$newShortSha := ShortSha .Comment.NewCommit}}
 				{{$newCommitLink := HTMLFormat "<a href='%[1]s'><b>%[2]s</b></a>" $newCommitUrl $newShortSha}}
 
-				{{.locale.Tr "mail.issue.action.force_push" .Doer.Name .Comment.Issue.PullRequest.HeadBranch $oldCommitLink $newCommitLink}}
+				{{.locale.Tr "mail.issue.action.force_push" .Doer.DisplayNameWithFullName .Comment.Issue.PullRequest.HeadBranch $oldCommitLink $newCommitLink}}
 			{{else}}
-				{{.locale.TrN (len .Comment.Commits) "mail.issue.action.push_1" "mail.issue.action.push_n" .Doer.Name .Comment.Issue.PullRequest.HeadBranch (len .Comment.Commits)}}
+				{{.locale.TrN (len .Comment.Commits) "mail.issue.action.push_1" "mail.issue.action.push_n" .Doer.DisplayNameWithFullName .Comment.Issue.PullRequest.HeadBranch (len .Comment.Commits)}}
 			{{end}}
 		</p>
 	{{end}}
 	<p>
 		{{if eq .ActionName "close"}}
-			{{.locale.Tr "mail.issue.action.close" .Doer.Name .Issue.Index}}
+			{{.locale.Tr "mail.issue.action.close" .Doer.DisplayNameWithFullName .Issue.Index}}
 		{{else if eq .ActionName "reopen"}}
-			{{.locale.Tr "mail.issue.action.reopen" .Doer.Name .Issue.Index}}
+			{{.locale.Tr "mail.issue.action.reopen" .Doer.DisplayNameWithFullName .Issue.Index}}
 		{{else if eq .ActionName "merge"}}
-			{{.locale.Tr "mail.issue.action.merge" .Doer.Name .Issue.Index .Issue.PullRequest.BaseBranch}}
+			{{.locale.Tr "mail.issue.action.merge" .Doer.DisplayNameWithFullName .Issue.Index .Issue.PullRequest.BaseBranch}}
 		{{else if eq .ActionName "approve"}}
-			{{.locale.Tr "mail.issue.action.approve" .Doer.Name}}
+			{{.locale.Tr "mail.issue.action.approve" .Doer.DisplayNameWithFullName}}
 		{{else if eq .ActionName "reject"}}
-			{{.locale.Tr "mail.issue.action.reject" .Doer.Name}}
+			{{.locale.Tr "mail.issue.action.reject" .Doer.DisplayNameWithFullName}}
 		{{else if eq .ActionName "review"}}
-			{{.locale.Tr "mail.issue.action.review" .Doer.Name}}
+			{{.locale.Tr "mail.issue.action.review" .Doer.DisplayNameWithFullName}}
 		{{else if eq .ActionName "review_dismissed"}}
-			{{.locale.Tr "mail.issue.action.review_dismissed" .Doer.Name .Comment.Review.Reviewer.Name}}
+			{{.locale.Tr "mail.issue.action.review_dismissed" .Doer.DisplayNameWithFullName .Comment.Review.Reviewer.DisplayNameWithFullName}}
 		{{else if eq .ActionName "ready_for_review"}}
-			{{.locale.Tr "mail.issue.action.ready_for_review" .Doer.Name}}
+			{{.locale.Tr "mail.issue.action.ready_for_review" .Doer.DisplayNameWithFullName}}
 		{{end}}
 
 		{{- if eq .Body ""}}
 			{{if eq .ActionName "new"}}
-				{{.locale.Tr "mail.issue.action.new" .Doer.Name .Issue.Index}}
+				{{.locale.Tr "mail.issue.action.new" .Doer.DisplayNameWithFullName .Issue.Index}}
 			{{end}}
 		{{else}}
 			{{.Body}}
diff --git a/templates/shared/user/name.tmpl b/templates/shared/user/name.tmpl
index 0bebd4e744e..a4744a6bdb6 100644
--- a/templates/shared/user/name.tmpl
+++ b/templates/shared/user/name.tmpl
@@ -1 +1 @@
-<a class="text muted" href="{{.HomeLink}}">{{.Name}}{{if .FullName}} ({{.FullName}}){{end}}</a>{{template "shared/user/user_type_label" .}}
+<a class="text muted" href="{{.HomeLink}}">{{.DisplayNameWithFullName}}</a>{{template "shared/user/user_type_label" .}}