The Squirrel with the Marvelous Tail (Swedish: Ekorren med den vackra svansen) is a small absentminded squirrel appearing in Moominland Midwinter. He has a bad memory and attention span, having to repeat things out loud to remember them. The squirrel is also a bit vain, greatly admiring its bushy tail for which it has named itself. He is notable for being one of the only characters in the books to die.
Early in Moominland Midwinter, he is introduced while searching for a mattress by the sea. In his search he goes into the cave and stumbles upon Little My and the Mymble's Daughter hibernating in a box. He accidentally wakes Little My up, who yells at him and angrily leaves the cave.
Later on, Too-ticky interrupts the squirrel while searching for a lost pine cone, warning him about the Great Cold and stressing how important it is for him to stay indoors the following night. However, the squirrel forgets Too-tickys warning and encounters the Lady of the Cold upon her arrival, whose gaze freezes him to death. The event is witnessed by Moomintroll and company from the bath house. After the Lady of the Cold leaves, Too-ticky steps out to try to thaw the squirrel, but finds it's too late. Moomintroll is distressed by the death of the squirrel, but is comforted by Too-ticky explaining how the squirrel eventually will turn into earth, where trees will grow and new squirrels frolic. Little My isn't phased at all by the squirrels passing, all she wants is to use its tail to make a muff, which Moomintroll forbids her from doing. A funeral is held for the squirrel, but the frozen ground makes it impossible to bury him. Instead, Moomintroll gets unexpected help from the snow horse built by Too-ticky for the Lady of the Cold, who has mysteriously come to life. The horse walks the company to the beach, where it takes the squirrel and gallops towards the horizon.
By the end of the book, when spring is returning to the valley, Moomintroll meets a new squirrel who also calls itself The Squirrel with the Marvelous Tail. He seems to have just as bad a memory as the first squirrel, as he can't recall if he meet the Lady of the Cold or not. Moomintroll says that he has to look into the subject closer another time, but apart from briefly talking about the subject to Moominmamma when she wakes from her winter sleep, this is never brought up again, leaving it ambiguous whether this is the same squirrel or another one.
- The Squirrel makes an appearance in the 1973 Swedish series Moominvalley and in the polish television series The Moomins very much like in the book.
- The Tanoshii Mūmin Ikka anime series completely omits the squirrel from the episodes based upon Moominland Midwinter, however in a number of other episodes there appears two other squirrels with the same design.