unknown, possibly Magnus III, the last Norse king of Mann, as the triskelion was in his coat of arms.
The Flag of the Isle of Man (Manx: Ellan Vannin) is a flag with a red background with a triskelion in the centre. a triskelion is a symbol consisting of three protrusions with threefold symmetry. in the case of this flag, the protrusions are counter-clockwise bent legs with spurs.
There are many theories on what the manx triskelion represents. One theory is that the three legs facing every direction represent the motto of the isle of man, "quocunque jeceris stabit" (wherever you throw it, it will stand.) another theory is that the triskelion represents the Celtic Sea God, Mannanin, who in manx mythology was the protector of the isle of man. It is said that Mannanin turned into three legs to combat saint patrick and assert himself over his people. It is also possible that both are correct, as the motto of the Isle of Man is what Mannanin proclaimed after changing into the three legs. Manx people will often tell you out of humour that the flag has counter-clockwise facing legs so that they are unable to kneel to the British.
Civil Ensign of the Isle of Man
Flag of the Lieutenant Governer of the Isle of Man