Yes, He is. The bread and wine become (when a Catholic priest prays the words of consecration during Mass) the very Body and Blood of Jesus Christ.

Firstly, how do we know this? Well, there are 2 primary ways:

Jesus said so. At the Last Supper, Jesus said, “This IS My Body ; this IS My Blood. Do this in remembrance of Me.” And so a perpetual sacrifice (a.k.a. the Mass) was established by Christ, to be repeated countless times daily in Catholic churches around the world. Indeed, it is estimated that every second of every day, 4 consecrations are being prayed at Masses

Innumerable miracles have been reported relating to Holy Communion over the past 2,000 years, such as:

Blood dripping from consecrated Hosts

Priests hiding Hosts from Nazis, & the Hosts’ disappearing before being found

Hosts being stolen from churches, and then floating back to the church

Priests burying Hosts to keep them from the Nazis, and decades later farm animals stopping over spot and standing there until Hosts were dug up

Secondly, it can be hard to believe that what looks and tastes like bread and wine is actually the Body and the Blood of Our Lord. But maybe that’s the point. God gave us our 5 senses, but sometimes they can deceive us. And so sometimes we must go beyond our senses, trusting that God says what He means and means what He says, even when we can’t perceive it.

Lastly, what about those Protestant denominations that still practice communion (under some form or another)? Well, certainly theirs are beautiful reminders of Jesus’s Last Supper, and of His sacrifice on the Cross. But because they have chosen to break away from the Apostolic Succession of the Catholic Church, their communion does not possess the Real (i.e., literal) Presence of Jesus in His very Body and Blood. (Apostolic Succession means that the Catholic Church can trace every one of her deacons/priests/bishops back to Jesus’s original 12 Apostles, who were ordained as the first priests by Jesus Himself at the Last Supper.)