The interpretation timeline
Mark 16:5 Douay-Rheims

And entering into the sepulchre, they saw a young man sitting on the right side, clothed with a white robe: and they were astonished.

A.D. 430 – 1849 8 witnesses 10 excerpts

Patristic

before A.D. 750
date
unknown
Severian of Gabala Patristic
fl. c. A.D. 400
“(Chrysologus ubi sup.) The women, then, entered the sepulchre, that being buried with Christ, they might rise again from the tomb with Christ. They see the young man, that is, they see the time of the Resurrection, for the Resurrection has no old age, and the period, in which man knows neither birth nor death, admits of no decay, and requires no increase. Wherefore what they saw was a young man, not an old man, nor an infant, but the age of joy.”
Source
“(Chrysologus ubi sup.) Again, they saw a young man sitting on the right, because the Resurrection has nothing sinister in it. They also see him dressed in a long white robe; that robe is not from mortal fleece, but of living virtue, blazing with heavenly light, not of an earthly dye, as saith the Prophet, Thou deckest thyself with light as with a garment; and of the just it is said, Then shall the righteous shine forth as the sun. (Ps. 104:2) (Matt. 13:43)”
Source
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“(ubi sup.) Either let us suppose that Matthew was silent about that Angel, whom they saw on entering, whilst Mark said nothing of him, whom they saw outside sitting on the stone, so that they saw two and heard severally from two, the things which the Angels said concerning Jesus; or we must understand by entering into the sepulchre, their coming within some inclosure, by which it is probable that the place was surrounded a little space before the stone, by the cutting out of which the burial place had been made, so that they saw sitting on the right hand in that space him whom Matthew designates as sitting on the stone.”
Source
604
A.D.
Gregory the Great Patristic
c. A.D. 540–604
“(ubi sup.) But the women who came with spices see the Angels; because those minds who come to the Lord with their virtues, through holy desires, see the heavenly citizens. Wherefore it goes on: And entering into the sepulchre, they saw a young man sitting on the right side, clothed in a long white garment; and they were affrighted.”
Source
“(ubi sup.) Or else, he appeared covered with a white robe, because he announced the joys of our festivity, for the whiteness of the robe shews the splendour of our solemnity.”
735
A.D.
Bede the Venerable Patristic
c. A.D. 672–735
“(ubi sup.) Now they saw a young man sitting on the right side, that is, on the south part of the place where the body was laid. For the body, which was lying on its back, and had its head to the west, must have had its right to the south.”

Scholastic

c. 1100 – 1500
1107
A.D.
c. 1055–1107
“Though Matthew says that the Angel was sitting on the stone, whilst Mark relates that the women entering into the sepulchre saw a young man sitting, yet we need not wonder, for they afterwards saw sitting within the sepulchre the same Angel as sat without on the stone.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And entering into the sepulchre,.... For the sepulchres of the Jews were made so large, that persons might go into them: the rule for making them is this (k); "he that sells ground to his neighbour to make a burying place, or that receives of his neighbour to make a burying place, must make the inside of the cave four cubits by six, and open in it eight graves; three here, and three there, and two over against them: and the graves must be four cubits long, and seven high, and six broad. R. Simeon says, he must take the inside of the cave six cubits by eight, and open within thirteen graves: four here, and four there, and three over against them; and one on the right hand of the door, and one on the left; and he must make, "a court", at the mouth of the cave, six by six, according to the bier, and those that bury; and he must open in the midst of it two caves, one here and another there. R. Simeon says, four at the four sides; R. Simeon ben Gamaliel says, all is according to the nature of the rock.'' Now it was in the court that the women entered, where the bier was to be put down by the bearers; and where they could look into the sepulchre, and the several caves and graves in it, and what were in them. So Maimonides says (l), "they dig caves in the earth, and make a grave on, the side of the cave, and bury in; it.'' And there being a door into one of these caves, persons might enter in, and see where the graves were, and the bodies lay. They saw a young man; an angel; as angels used to appear in the form of men: nor is this any contradiction to John's account, who says there were two angels, one at the head, and another at the feet, Joh 20:12; since Mark does not say there was no more than one; besides, John relates what Mary Magdalene saw, when alone, and Mark what all the women saw: sitting on the right side; from whence we learn, on what side of the door of the sepulchre Christ was laid, according to the above description of one: clothed long white garment: See Gill on Mat 28:3; which was as white as snow: and they were affrighted; at the sight of him; not expecting such a vision, but to have seen, the body of their Lord. (k) Misn. Bava Bathra, c. 6. sect. 8. (l) Maimon. Hilch. Ebel, c. 4. sect. 4.”
Source
1849
A.D.
1774–1849
“St. Matthew says the angel was sitting on the stone, whilst St. Mark says that they saw him sitting on the right side of the sepulchre. This must not surprise us; for the angel which first appeared sitting upon the stone, might have been afterwards seen by him sitting on the right side of the sepulchre. (Theophylactus) — Perhaps the angel mentioned by St. Matthew is different from the one mentioned by St. Mark. Or it may be understood, that the women entering the monument, which may mean the enclosure of it, saw the angel sitting on the stone, which was placed on the right side of the sepulchre. (St. Augustine)”
Source

Undated

date unknown
date
unknown
“The white robe is also true joy, now that the enemy is driven away, the kingdom won, the King of Peace sought for and found and never let go by us. This young man then shews an image of the Resurrection to them who feared death. But their being frightened shews that eye hath not seen, nor ear heard, neither have entered into the heart of man to conceive the things which God hath prepared for them that love Him. (1 Cor 2:9) There follows, And he saith unto them, Be not affrighted.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.