The Number 1 symbolizes the start, the beginning of things. It represents the being, personal identity, leadership and above all the personal resources and the ability to use them. On the negative side It is related with the possession, the selfish and the martyr.
In Tarot, guides us to success, obtained or to be obtained. And as a result is always a look of triumph.
In the Major Arcana, The Magician is the one that best represents the qualities of this number.
In Astrology corresponds to The Sun.