The Personality of Deity
So, there are different levels of Buddhas. There are also different classes of Buddhas, and different vows and promises and specializations as you might guess. If we think about the myriad beneficial activities of the buddhas and bodhisattvas, there must be some kind of overarching motivating principle that has a penchant for organizing and creation dharmic specialization fueled by the needs of sentient beings.
There are formal vows taken by high level beings bestowed by even higher level Buddhas or self taken promises to achieve certain results for themselves or others in need. The experiences and tendencies that come from these vows also produce further activity. For example, Vajrasattva, the Buddha of purification took vows and made promises to help living beings purify. Green Tara and White Tara, have different specializations, different kinds of vows and promises for activities from each other as well as different than Vajrasattva. So it is not just their interest that produced the experiences of a deity. Perhaps there is something else that could be called higher karma.
For example, by his vow, Vajrasattva is alert for opportunities to benefit others and experiences the activity of his work in purifying beings. In doing that he produces a kind of a high karma that causes him to be called upon again to do purifying. It is a positive feedback loop, so Vajrasattva helps people purify, and he is so good at it that they tell other people who also pray and request Vajrasattva to purify.
The purification facilitated by the Buddha Vajrasattva is comprised not only of deity, but personality, and deity always has personality. Deity has a cultivated personality. The tantric practitioner visualizes the deity as pleased with their efforts but the deity actually has opinions also. Deity is a personification of the absolute level that also produces personality.
So, now we might think a Buddha possesses personality. Yes. Is that all that a Buddha is? No. So, we could say that Buddha can indeed be a deity. A Buddha is a deity, and in fact, in Tibetan Buddhism, we have many Buddha deities. These are real living beings. They do not remain only sitting holding a hand this way and holding a hand that way, or one foot in the air or however they are depicted in the iconography, they are not static. They are real living beings. They are real Buddhas. It's good? It's very good. We are very lucky. We are very lucky in this world to be the recipients of the interest of the Buddhas in whatever form they come.