From the Greek name Αλεξις which meant "helper" or "defender", derived from Greek αλεξω "to defend, to help". This was the name of a 3rd-century BC Greek comic poet, and also of several saints. It is used somewhat interchangeably with the related name Αλεξιος or Alexius, born by five Byzantine emperors.
The greatest of the greatest. If you think that you have found anyone better than Aleksejus, think again. No person, animal or thing is better than Aleksejus.