Who is the most recent saint recognized by both the Catholic and the Orthodox churches?

I believe that the correct answer would be either Abraham of Rostov, who died between 1073 and 1077; or Antony (Anthony) of the Caves, who died in 1073. Both appear in the list of Catholic saints, and both are venerated in the Eastern Orthodox Church.

Abraham is known as Abraham the Wonderworker in the Orthodox Church, where he is remembered on October 29. His life is described:

Saint Abramius, Archimandrite of Rostov, in the world Abercius, left his parents’ home in his youth and entered upon the path of Christian asceticism. Having assumed the monastic schema, Abramius settled at Rostov on the shore of Lake Nero. In the Rostov lands there were not many pagans, and the saint worked intensely at spreading the true Faith.

Not far from the cell of the saint was a pagan temple, where the pagans worshipped a stone idol of Veles (Volos), which caused fright among the inhabitants of Rostov. In a miraculous vision the Apostle John the Theologian stood before Abramius, and gave him a staff with a cross on top, with which the venerable one destroyed the idol. At the place of the pagan temple, St Abramius founded a monastery in honor of the Theophany and became its head.

In memory of the miraculous appearance, the holy monk built a church named for St John the Theologian. Many of the pagans were persuaded and baptized by St Abramius. Particularly great was his influence with the children whom he taught the ability to read and write, instructing them in the law of God, and tonsured monastics from among them.

Everyone who came to the monastery was accepted with love. The saint’s life was a constant work of prayer and toil for the benefit of the brethren: he chopped firewood for the oven, he laundered the monks’ clothing and carried water for the kitchen. St Abramius reposed in old age and was buried in the church of the Theophany.

His holy relics were uncovered in the time of Great Prince Vsevolod (1176-1212). In the year 1551, Tsar Ivan the Terrible, before his campaign against Kazan, made the rounds of holy places. At the Theophany-Abramiev monastery the monks showed him the staff with which St Abramius had destroyed the idol of Veles. The Tsar took the staff with him on the campaign, but the cross remained at the monastery. And returning again after the subjugation of the Khan, Ivan the Terrible gave orders to build a new stone church at the Abramiev monastery in honor of the Theophany, with four chapels, and he also supplied it with books and icons.

The life of Antony of the Caves is described:

Saint Anthony of the Kiev Caves was born in the year 983 at Liubech, not far from Chernigov, and was named Antipas in Baptism. Possessing the fear of God from his youth, he desired to be clothed in the monastic schema. When he reached a mature age, he wandered until he arrived on Mt. Athos, burning with the desire to emulate the deeds of its holy inhabitants. Here he received monastic tonsure, and the young monk pleased God in every aspect of his spiritual struggles on the path of virtue. He particularly excelled in humility and obedience, so that all the monks rejoiced to see his holy life.

The igumen saw in St Anthony the great future ascetic, and inspired by God, he sent him back to his native land, saying, “Anthony, it is time for you to guide others in holiness. Return to your own Russian land, and be an example for others. May the blessing of the Holy Mountain be with you.

Returning to the land of Rus, Anthony began to make the rounds of the monasteries about Kiev, but nowhere did he find that strict life which had drawn him to Mt. Athos.

Through the Providence of God, Anthony came to the hills of Kiev by the banks of the River Dniepr. The forested area near the village of Berestovo reminded him of his beloved Athos. There he found a cave which had been dug out by the Priest Hilarion, who later became Metropolitan of Kiev (October 21). Since he liked the spot, Anthony prayed with tears, “Lord, let the blessing of Mt. Athos be upon this spot, and strengthen me to remain here.” He began to struggle in prayer, fasting, vigil and physical labor. Every other day, or every third day, he would eat only dry bread and a little water. Sometimes he did not eat for a week. People began to come to the ascetic for his blessing and counsel, and some decided to remain with the saint.

Among Anthony’s first disciples was St Nikon (March 23), who tonsured St Theodosius of the Caves (May 3) at the monastery in the year 1032.

The virtuous life of St Anthony illumined the Russian land with the beauty of monasticism. St Anthony lovingly received those who yearned for the monastic life. After instructing them how to follow Christ, he asked St Nikon to tonsure them. When twelve disciples had gathered about St Anthony, the brethren dug a large cave and built a church and cells for the monks within it.

After he appointed Abbot Barlaam to guide the brethren, St Anthony withdrew from the monastery. He dug a new cave for himself, then hid himself within it. There too, monks began to settle around him. Afterwards, the saint built a small wooden church in honor of the Dormition of the Mother of God over the Far Caves.

At the insistence of Prince Izyaslav, the igumen Barlaam withdrew to the Dimitriev monastery. With the blessing of St Anthony and with the general agreement of the brethren, the meek and humble Theodosius was chosen as igumen. By this time, the number of brethren had already reached a hundred men. The Kiev Great Prince Izyaslav (+ 1078) gave the monks the hill on which the large church and cells were built, with a palisade all around. Thus, the renowned monastery over the caves was established. Describing this, the chronicler remarks that while many monasteries were built by emperors and nobles, they could not compare with those which are built with holy prayers and tears, and by fasting and vigil. Although St Anthony had no gold, he built a monastery which became the first spiritual center of Rus.

For his holiness of life, God glorified St Anthony with the gift of clairvoyance and wonderworking. One example of this occurred during the construction of the Great Caves church. The Most Holy Theotokos Herself stood before him and St Theodosius in the Blachernae church in Constantinople, where they had been miraculously transported without leaving their own monastery. Actually, two angels appeared in Constantinople in their forms (See May 3, the account of the Kiev Caves Icon of the Most Holy Theotokos). Having received gold from the Mother of God, the saints commissioned master architects, who came from Constantinople to the Russian land on the command of the Queen of Heaven to build the church at the Monastery of the Caves. During this appearance, the Mother of God foretold the impending death of St Anthony, which occurred on July 10, 1073.