indefatigable, tireless, unflagging, unwearying
Meaning: showing sustained enthusiastic action with unflagging vitality; "an indefatigable advocate of equal rights"; "a tireless worker"; "unflagging pursuit of excellence"
Then Trotzky again, fiery, indefatigable, giving orders, answering questions.
The fire-fighters meanwhile kept up their indefatigable work under the direction of the Mayor and the chief of their department.
She was an indefatigable student: constantly reading and learning; with a strong conviction of the necessity and value of education, very unusual in a girl of fifteen.
These are the only two instances I have met with of talking dogs, but my brother had a beautiful little spaniel, named Doll, who was an indefatigable hunter after woodcocks and snipes.
Her cloister of vaulted passages enables her to proceed to any point of the star-shaped pouch containing the eggs. Indefatigable in her rounds, she stops here and there; she fondly feels the satin, listens to the secrets of the wallet.