Sylvester Stallone's dog Butkus helped him launch his acting career.

The 70-year-old actor has taken to social media to gush about his four-legged friend, which saw him credit his pet as the one who helped him to write the 1976 movie 'Rocky', which propelled him into the entertainment industry.

Alongside a picture of him holding his furry friend on his lap when he was just a puppy, which has been shared on his Instagram account, he wrote: ''1971... Since we're on the subject of '' man's best friend'' this is myself and Butkus as a puppy , we were both , thin , hungry and living in a flophouse above a subway stop, I used to say this apartment had ' ... Hot and cold running roaches' anyway there was not much to do except spend time with each other and that's where I started to learn the craft of screenwriting. Since I never went out, I relied on his companionship , And actually it was his idea to write Rocky, but don't tell anyone... (sic).''

Sylvester reflected on the ''modern day miracle'' in the sweet upload in which he has admitted he was forced to sell the Bull Mastiff for $40 to help him survive, although he later bought back his beloved friend for $15,000 following the success of his sport action film.

The American star - who has children Seargeoh, Scarlet, 14, Sistine, 18, and Sophia, 20 - continued: ''Years later when things got even worse I had to sell him for $40 in front of a 7-Eleven store,because I couldn't afford food, then like A modern day miracle, the screenplay for Rocky sold, and I could buy and buy him back, but the new owner knew I was desperate, and charged me $15,000 ... He was worth every penny! #New York City #HellsKitchen #BullMastiff #It'sADogsWorld. #MoreToCome#inspiration #ThunderingYourHeart #GoingThedistance (sic).''

And the 'Creed' star has thanked his ''best friend, my confidant'' for enduring the hardship of being ''totally broke'' with him when he was in his 20s.

Alongside a sweet picture of the movie icon cradling his pooch, which was edited with a black and white filter, and shared on his photo-sharing site, he wrote: ''I absolutely love pictures like this. When I was 26, totally broke, going nowhere VERY fast, owned two pair of pants that barely fit, shoes that had holes in them and dreams of being successful were as far away as the sun... But I had my dog, BUTKUS, my best friend, my confidant, Who always laughed at my jokes, and put up with my moods, and was the one living thing that loved me for who I was! #man's best friend#BullMastiff #Loyalty #NewYorkCity#AmericanDreams (sic).''