Moominpappa (Swedish: Muminpappan) is a Moomin married to Moominmamma and is the father of Moomintroll. Orphaned in his youth, Moominpappa is a somewhat restless soul who left the orphanage to venture out into the world with his friends Hodgkins, The Muddler and the Joxter, but has now settled down, determined to be a responsible father to his family: his wife Moominmamma and their son Moomintroll. He is almost always wearing his black top-hat, inside which is painted, "M.P. from your M.M." to differentiate it from all the other top hats in the world.
In his childhood, Moominpappa felt very misunderstood by the strict Hemulen headmistress at the orphanage, and after falling down an ice-hole while admiring his own reflection he decided to explore the world on his own and become a famous explorer.
He fled the orphanage and after wandering through a dark and scary forest he found a person sitting next to a water-wheel in a brook. The person presented himself as the inventor Hodgkins, and told Moominpappa that he will use the water-wheel construction on his riverboat. Hodgkins then showed him the unfinished ship as well as his nephew, The Muddler, and friend The Joxter. Together all four of them finished the boat, The Oshun Oxtra (the Muddler was supposed to write "The Ocean Orchestra"). They launched the ship by tricking Edward the Booble into overflowing the river. Then Moominpappa and his friends travelled downriver to the sea, where he saved the Hemulen's aunt from being eaten by the Groke, but she gets attacked by Niblings.
Thereafter they found an island were they befriended the Mymble's family and celebrated the King of the island's 100th birthday, where they all won prizes. Hodgkins got an offer by the king to become court inventor, and Moominpappa stayed on the island, although he really wanted to go on more adventures with Hodgkins, and rebuilt the navigation hut of the Oshun Oxtra into a house for himself. Then Hodgkins constructed an upgraded version of their ship, able to travel through land, sea and sky, and invited his friends on its maiden voyage. They got attacked by a sea-monster, but they saved when Edward the Booble accidentally stepped on it. Some time later Moominpappa saved Moominmamma from drowning.
According to his family, he writes down all of his adventues in a book called "Memoirs". He once commented that because so many adventures happen to him, he might never finish the book.According to Moomintroll, Moominpappa can fix anything if he is able to get around to it. He sometimes feels a secret longing to live with the Hattifatterners, something that is explored in a short story in Tales from Moominvalley. He is also shown to be friends with most adventurous characters in Moominvalley, such as Wimsy, and even Stinky.