Remove Site Collection Administrator using PowerShell

How to remove a site collection administrator in SharePoint? To remove SharePoint Site Collection Administrator, we use "Site collection Administrators" link from site settings.
You must be a Farm Administrator or site collection administrator to see this link, BTW! From this page, we can delete site collection administrators.

PowerShell Script to Remove Site Collection Administrator:
We may have to remove site collection administrators programmatically. Lets use PowerShell in SharePoint to remove site collection administrator:

Function RemoveSiteCollAdmin($AdminID, $SiteCollectionURL)
 {
 #Get the site collection
 $site = Get-SPSite $SiteCollectionURL

 #Get the Admin to remove from Site collection Administrator Group
 $Account = $site.RootWeb.SiteAdministrators | where {$_.UserLogin -eq $AdminID}
 
    #if User account found
 if($Account)
 {
  $Account.IsSiteAdmin = $false
  $Account.Update()
  Write-Host "$($AdminID) has been removed from Site Collection Administrator Group!"
 }
 else
 {
  Write-Host "$($AdminID) Not found in Site Collection Administrator Group!"
 }
}

 #Call the function to remove Site collection Admin
 RemoveSiteCollAdmin "Domain\UserAccount" "http://sharepoint.crescent.com/"

Note that, Primary Site collection administrator can't be removed and can be only changed! If you want to change a Primary Site collection administrator using Central Administration/PowerShell/Stsadm tool, refer my post: How to Change Site Collection Primary, Secondary Administrators in SharePoint