(c. 257-c. 288)
St. Sebastian was an officer in the Roman army, esteemed even by the heathen as a good soldier, and honored by the Church ever since as a champion of Jesus Christ. Born at Narbonne (France), Sebastian came to Rome about the year 284, and entered the lists against the powers of evil. He found the twin brothers Marcus and Marcellinus in prison for the faith, and, when they were near yielding to the entreaties of their relatives, encouraged them to despise flesh and blood, and to die for Christ. God confirmed his words by miracle: light shone around him while he spoke; he cured the sick by his prayers; and in this divine strength he led multitudes to the faith, among them the Prefect of Rome, with his son Tiburtius. He saw his disciples die before him, and one of them came back from heaven to tell him that his own end was near. It was in a contest of fervor and charity that St. Sebastian found the occasion of martyrdom.
The Prefect of Rome, after his conversion, retired to his estates in Campania, and took a great number of his fellow-converts with him to this place of safety. It was a question whether Polycarp the priest or St. Sebastian should accompany the neophytes. Each was eager to stay and face the danger at Rome, and at last the Pope decided that the Roman church could not spare the services of Sebastian. He continued to labor at the post of danger till he was betrayed by a false disciple. He was led before Diocletian, and, at the emperor’s command, pierced with arrows and left for dead. But God raised him up again, and of his own accord he went before the emperor and conjured him to stay the persecution of the Church. Again sentenced, he was at last beaten to death by clubs, and crowned his labors by the merit of a double martyrdom.
Lives of the Saints, by Alban Butler, Benziger Bros. ed. 
Pope St Fabian (- 250)
He became Pope in 236 and was martyred on 20 January 250, during the persecution of the Emperor Decius. See the articles in Wikipedia and the Catholic Encyclopaedia.
Nothing is known about St Sebastian except the fact that he was martyred early on in the persecutions of Diocletian. St Ambrose knew of him and states that he was already venerated in Milan in the fourth century. One of the seven chief churches of Rome was built over his grave in 367.
All else (his youth, his martyrdom by arrows) is fiction, some of it dating from more than a thousand years after his death. But what we know is what we need to know. For the Christians of the fourth century the important, the true, the sufficient fact about Sebastian was that he was a martyr, and they venerated him as such. It should be enough for us as well. See the article in the Catholic Encyclopaedia.
Other saints: Blessed Cyprian Michael Tansi (1903 – 1964)
Father Cyprian Michael Iwene Tansi was born in Nigeria in 1903. He was brought up by the Holy Ghost Fathers (Spiritans) and trained as a teacher and a catechist. Later he decided to join the seminary and in 1937 he was ordained a priest. In 1950 he left his Diocese in order to go to England where he joined the Cistercian Abbey of Mount St Bernard, near Nottingham. He had been singled out as the ideal candidate to be trained in England and then return to establish a Trappist Monastery in the Diocese of Onitsha in Nigeria. Fr Tansi lived the monastic life with great faith and humility. Absorbed in prayer, he was a living example of patience and charity. Early in 1964 he was diagnosed with aortic aneurysm and died two weeks later on 20 January 1964. See the article in Wikipedia.
You will see these texts in a more readable format and with a better layout (especially for verse) if you use the free Catholic Calendar app from Universalis.
Catholic Calendar is free.
You may also be interested in the full Universalis app.
The official Grail translation of the Psalms.
The readings at Mass are in both the Jerusalem Bible/Grail and the NAB translations.
The “Mass Today” page contains the exact liturgy for today all in one place, both the Order of Mass and the prayers, antiphons and readings.
A perpetual liturgical calendar covering all years.
Local liturgical calendars for over 20 countries and dioceses.
A choice of views: either scrolling like a web page or page-turning like an e-book.
Access to all texts for all dates, past, present and future.
Complete independence from the Internet. Everything is stored within the application itself.
Universalis costs £9.99 / $13.99 / €12.99 from the App Store.
Alternatively you can pay nothing to start with and then subscribe for £0.69 / $0.99 / €0.89 per month. To do this, get the free Catholic Calendar app and press the “Try or buy” button in the calendar.