Question: Which two individuals was Leonardo da Vinci having a difficult time depicting in "The Last Supper"?
About the article "Leonardo da Vinci", section "Paintings of the 1490s".

Candidate passages:
In 1447 he worked in the refectory of Sant'Apollonia in Florence, painting, in the lower part, Last Supper fresco, accompanied by other scenes portraying the Deposition, Resurrection, and Crucifixion, which are now damaged.
He also painted a lunette in the cloister, depicting a "Pietà".
The "Last Supper" displays del Castagno's talents at his best.
The detail and naturalism of this fresco portray the ways in which del Castagno departed from earlier artistic styles.
It is likely that Leonardo da Vinci was already familiar with this work before he painted his own Last Supper in a more dramatic form to contrast with the stillness of these works, so that more emotion would be displayed. 
References in other media.
Novels and short stories.
"The Da Vinci Code".
This work of fiction has been the centre of controversy over the accuracy of its depictions of Christianity and of da Vinci.
A bestselling 2003 novel by Dan Brown, adapted and released as a major motion picture in 2006, "The Da Vinci Code" revolves around a conspiracy based on elements of Leonardo's "Last Supper" and other works.
A preface to the novel claims that depictions of artworks, secret societies and rites described within the novel are factual.
For this reason much of the content of the novel has been widely accepted by readers as authoritative.
Because the theme involves a conspiracy within the Church over the life of Jesus and the suggestion that the Church has hidden the facts of his marriage, there has been a strong reaction against the novel and much material published examining and refuting its claims.
Within the novel it is claimed that from 1510–1519, Leonardo was the Grand Master of a secret society, the Priory of Sion.
In reality this society existed only as a 20th-century hoax, but author Dan Brown used as a source the 1982 pseudohistory book "The Holy Blood and the Holy Grail".
The writers of this book had based their research on forged medieval documents that had been created as part of the Priory of Sion fraud.
The mix of fact and fiction in the documents made it difficult to discount immediately as a forgery.
For example, it was claimed that the Grand Master prior to Leonardo was Botticelli, who had indeed had an association with Leonardo, as they were both students at the Florence workshop of Andrea del Verrocchio.
The Priory of Sion story and the veracity of "The Holy Blood and the Holy Grail" was eventually debunked, and many of those involved publicly recanted, although Dan Brown continued to assert that the facts as presented were true.
In portraying the Priory of Sion as "fact" "The Da Vinci Code" expanded on the claims in "The Holy Blood and the Holy Grail":  That there were additional secrets hidden in Leonardo's paintings, such as an "M" letter in the painting of The Last Supper, indicating the presence of Mary Magdalene and that the figure to the left of Jesus traditionally said to represent John the Evangelist actually represents Mary Magdalene.
That the "Mona Lisa" was actually a self-portrait.
That among the differences in the two versions of the painting of the "Virgin of the Rocks" which hang in the Louvre and London's National Gallery, is the fact that in the Louvre painting the baby to the left of the picture depicts Jesus, and to the right John the Baptist, rather than the accepted view, which is the other way round.
That Leonardo invented a cryptex for carrying secret messages.
The book also used a variation of Leonardo's backwards handwriting to hide a secret message on the American bookjacket.
Among the many criticisms of Brown's writing is that he uses the name da Vinci (meaning "from Vinci") in the manner that surnames are commonly used nowadays.
Leonardo would never have been referred to simply as "da Vinci" in his lifetime.
Such designations were appended to common baptismal names in order to identify individuals. 
Films which are about the life of Leonardo or in which he appears as a character:  "Leonardo Da Vinci" (1919), silent film "The Life of Leonardo da Vinci" (1971) starring Philippe Leroy as Leonardo da Vinci "Nothing Left to Do But Cry" (1984) starring Roberto Benigni and Massimo Troisi "Quest of the Delta Knights" (1993) depicting a fictional version of the young Leonardo  " Leonardo Da Vinci" (1996) – Animated movie  "Ever After" (1998) starring Drew Barrymore and Patrick Godfrey as Leonardo da Vinci  "Christie Malry's Own Double-Entry" (2000) starring Mattia Sbragia as Leonardo da Vinci  "Leonardo" (2003), TV movie starring Mark Rylance as Leonardo da Vinci Films which refer to Leonardo's works or inventions:  "Hudson Hawk" (1991) starring Bruce Willis and Danny Aiello revolves around Leonardo da Vinci's inventions "The Da Vinci Code" (2006) starring Tom Hanks "The Da Vinci Treasure" (2006) depicts Da Vinci's paintings as clues that lead to enlightenment  
Depictions of the Last Supper in Christian art:  "The Last Supper" (Leonardo da Vinci), the famous 1495–1498 painting by Leonardo da Vinci  "Last Supper" (del Castagno), a 1447 painting by Andrea del Castagno  "Last Supper", a 1464–1467 painting by Dirk Bouts  "Last Supper" (Ghirlandaio), a 1480 painting by Domenico Ghirlandaio  "Last Supper" (Tintoretto), a 1594 painting by Tintoretto  "The Last Supper", a 16th-century painting by Jacopo Bassano  "The Last Supper", a 1648 painting by Philippe de Champaigne  "Last Supper", a 1685 painting by Simon Ushakov  "Last Supper", a 17th-century painting by Nicolas Poussin  "The Last Supper", a 1721 painting by Gustavus Hesselius  "The Last Supper", an 1861 painting by Nikolai Ge  "Last Supper", a 1974 painting by Ultra Violet (Isabelle Collin Dufresne)  "The Sacrament of the Last Supper", by Salvador Dalí  "The Last Supper", a 1986 series of paintings by Andy Warhol  "The First Supper", a 1988 painting by Susan Dorothea White  "The Last Supper: Spirit, Flesh, Blood", 2006 series of paintings by Igor Kalinauskas  
Santa Maria delle Grazie ("Holy Mary of Grace") is a church and Dominican convent in Milan, northern Italy, included in the UNESCO World Heritage sites list.
The church contains the mural of "The Last Supper" by Leonardo da Vinci, which is in the refectory of the convent.