Who is Dante’s traveling companion though the Inferno, through Purgatory and through Paradise and why would Dante have chosen these companion?

La Divina Commedia (The Divine Comedy) is a fourteenth-century epic poem written by one of the most well-known Italian poets: Dante Alighieri. It consists of three parts: Inferno (Hell), Purgatorio (Purgatory), and Paradiso (Heaven). Essentially, The Divine Comedy is an allegory for the soul's journey towards God. Throughout the poem Dante makes a clear distinction between two separate personas: Dante the Pilgrim (the one who goes on a journey through Hell, Purgatory, and Heaven) and Dante the Poet (the one who wrote about the experiences of Dante the Pilgrim in Hell, Purgatory and Heaven). Dante the Pilgrim has two traveling companions who guide him through the three mythical places; the famed Ancient Roman poet Publius Virgilius Maro (or Virgil) is his guide through Hell and half of Purgatory, and his beloved Beatrice is his guide through the last four cantos of Purgatory and Heaven.
The wise Virgil appears to Dante in ghost form. Virgil is stuck in Hell because he died before the birth of Christ and is considered a pagan. Dante has a lot of respect for his fellow poet and even considers him an inspiration:

Thou art my master, and my author thou,Thou art alone the one from whom I tookThe beautiful style that has done honor to me.

This is why Dante, essentially, chooses Virgil as his guide and traveling companion through Hell and part of Purgatory. Virgil is, basically, Dante's mentor, and Dante shows the admiration he feels for the poet by making several references to Virgil's Aeneid.
As Virgil cannot enter Heaven or come close to it, Beatrice is the one who takes over his role as a guide to Dante. She appears to Dante as an angel, but she was apperently a real person named Beatrice Portinari, who came from a rich banking family. According to several sources, Dante had met Beatrice only twice in his life, but he was so fascinated by her beauty and grace that he fell in love with her deeply and instantly. This is why Dante chose her as his traveling companion in Heaven.
In The Divine Comedy, Beatrice is thought to represent the ideal woman and humanity's virtue, kindness, and faith in God. Dante alludes to the fact that he was able to endure his journey through Hell because he constantly thought of his love for Beatrice. Before starting the journey through Heaven, Beatrice informs Dante that he cannot enter if he is not cleansed of all sins.