Who he was - Rather "what sort of person," he was, or how he appeared. He had that curiosity which is natural to people to see one of whom they have heard much. It would seem, also, that in this case mere "curiosity" led to his conversion and that of his family. Compare 1-Corinthians 14:23-25. God makes use of every principle - of curiosity, or sympathy, or affection, or hope, or fear - to lead people in the way of salvation, and to impress truth on the minds of sinners.
The press - The crowd; the multitude that surrounded Jesus. Earthly princes are often borne in splendid equipages, or even carried, as in Eastern nations, in palanquins on the shoulders of people. Jesus mingled with the multitude, not seeking distinctions of that sort, and perhaps, "in appearance," not distinguished from thousands that followed him.
Little of stature - Short. Not a tall man.

And he sought to see Jesus who he was - So the mere principle of curiosity in him led to his conversion and salvation, and to that of his whole family, Luke 19:9.

And he sought to see Jesus who he was,.... What sort of a person he was for complexion, stature, and age: having heard much of him, he was very desirous of indulging his curiosity with a sight of him; having, as yet, nothing else that induced him to desire to see him: his desire to see Jesus was not of the same kind with the kings and prophets, Matthew 13:16 but rather like that of Herod, Luke 23:8
and could not for the press; the multitude of people that were flocking to meet Jesus, or who came before him, or were about him; for one part of the multitude went before him, and the other followed after him; so that he was in the crowd, and therefore could not easily be seen;
because he was little of stature. The Syriac and Persic versions read, "because Zacchaeus was little of stature", lest it should be thought that this is said of Jesus; for the reason why Zacchaeus could not see him for the crowd, was not because Christ was little of stature, and was hid among them, but because Zacchaeus was little of stature, and could not see over their heads.

who he was--what sort of person. Curiosity then was his only motive, though his determination not to be baulked was overruled for more than he sought.

Sought to see Jesus. Out of curiosity.
Climbed up into a sycamore tree. A kind of mulberry fig with low branches. His shortness of stature and the crowd made this necessary if he would see Jesus.