Most Christian denominations teach that the Holy Trinity is God the Father, God the Son and God the Holy Ghost (or Holy Spirit), three in one God. So, to a Christian there is a Holy Trinity.
However, the Holy Trinity is not referred to in the Bible. The concept of the Holy Trinity was adopted following the Council of Nicaea, held in 325 CE. Some would say that the Holy Trinity was a theological creation made necessary in the fourth century by the widespread popularity of Arianism.
It has long been recognized that many biblical passages refer clearly either to the trinity or to aspects of it. The oneness of God, together with the deity of Jesus Christ are taught repeatedly in scripture. There are a number of other doctrines or teachings in scripture, which, while clearly taught in scripture, either explicitly, or in principle, were not given prominence until a later date. Thus, it is rather irrelevant that some contend that the doctrine of the trinity was a creation of a later date when it is so clearly scriptural.
The formulations of the Council of Nicea are also probably irrelevant to the actual existence of the Holy Trinity. The Holy Trinity exists and has always existed from before the creation of the tri-universe of space, time and matter. Such a universe, reflective of the essence of the trinity, was also created as God, in His triunity said 'Let us...' He did not need to wait for any council of man but took His own creative and totally self-directed council. God is the creator, man, made in His image, is merely an 'explainer' after the fact.
All attacks on Jesus' divinity, such as are found in a number of modern cult systems also ineviatably involve an attack on the trinity. Together with this, they involve radical re-interpretations or denials of clear scriptural meanings. Nicea was merely a restatement of what was always taught in scripture. The scripture, as an expression, or outworking of God's will, reveals the details of the divine essence. Such revelation, if it means anything at all is either in accord with God's will or else it means nothing.