Emperor Pertinax is described as being the son of a slave who became Roman Emperor. However, that statement appears to be incorrect, according to the data above. Emperor Pertinax was descended from Arrius Piso via his daughter 'Antia', a.k.a. Arria Fadilla/Claudia Phoebe/Pompeia Plotina. Emperor Pertinax was the half-brother of Emperor Marcus Aurelius, as they had the same mother, but different fathers. Marcus Aurelius' father, Annius Verus III (aka Julianus Piso) died in 124 CE, and Marcus Aurelius was born in 121. Marcus Aurelius' mother had then given birth to Pertinax (Publius Helvius Pertinax) in 126 CE, his father being Antius Helvius Priscus Successus, who is described as a 'freedman'. But the term "freedman", in some instances, was used by a father regarding his son, because the son is in the father's bondage or charge until he is of age, and then 'freed'.
Some of the ancient authors used this term regarding their own sons, without stating it was their son they were referring to, so as to give the impression, or create the illusion, that slaves were being ‘freed’ for various reasons. This gave the slaves a (false) incentive to work towards their possible release from enslavement. Within academia, the study of inscriptions and coins is still not used universally. Many scholars are not able to read or understand all of the ancient languages necessary to make full use of coins and inscriptions. This also seems to be a reason why only a very small proportion of them know anything at all regarding the Jews of that time.
In his 'Roman Coins And Their Values' book (Fourth Revised Edition, 1988), David R. Sear gives a plethora of information about the Roman Emperors. Regarding Pertinax, for instance, he says "P. Helvius Pertinax was born at Alba Pompeia in A.D. 126, the son of a timber-merchant." On page 184, he says "He (Pertinax) had a successful military career and achieved senatorial rank until, at the death of Commodus, he was prefect of the City of Rome." He also says "He reluctantly accepted the throne when it was offered (to) him by the murderers of Commodus,..."
David Sear also says, "Flavia Titiana, wife of Pertinax, was the daughter of Flavius Sulpicianus. Her fate, following her husband's murder, in unknown." And, "Their son, Pertinax Junior, survived his father's downfall and was held in high esteem by Septimius Severus, who placed him in charge of a sacerdotal college. He (Pertinax Junior) eventually perished in Caracalla's massacre of the adherents of Geta in A.D. 212."
The above information answers the question as to what made Pertinax appear to be both a viable and better choice for emperor than Commodus in the eyes of his murderers. Commodus was the son of Marcus Aurelius a seemingly great and beloved emperor, but Commodus was nothing like his father.
Data regarding Emperor Pertinax can be found in the Historia Augusta, Loeb Classical Library edition - pg. 315, Publius Helvius Pertinax was the son of Helvius Successus - pg. 317, the mother of Pertinax died in Germany, in 167 CE - pg. 321, (after proconsulship) Pertinax was made "Prefect of the City" and succeeded Fuscianus in this office - pg. 325, Pertinax, given the name of 'Augustus' and also his wife Flavia Titiana was given the name (publicly) of Augusta - pg. 339, the two children of Pertinax, a son and daughter - pg. 343, the wife of Pertinax was Flavia Titiana, daughter of Flavius Sulpicianus (whom he let succeed him as Prefect of the City) - pg. 345, a nephew of Didius Julianus (the successor to the throne of Pertinax), was betrothed to the daughter of Pertinax - pg. 347, Pertinax was born August 1st of 126 CE and died March, 26th, 193 CE.
The Historia Augusta is a collection of biographies of the Roman emperors, written in Latin. The true authorship of the Historia Augusta, its actual date, reliability, and its purpose, have been a source of controversy amongst historians and scholars. It has been analyzed using computer algorithms, and the conclusion of those studies revealed that there was only one author instead of the six it has been attributed to. In his book, ‘Emperors and Biography’, Sir Ronald Syme stated: “When the attempt is made to expose a fraud, attack on all fronts is to be commended.” He concluded that, on a superficial level, the Historia Augusta was a deliberate fraud, and to understand what it really presents, different studying methods must be applied and was saying that, as historians, we cannot dismiss any methodology or piece of evidence, because a piece of information which may not seem vital, can prove crucial. All the individuals being discussed in the Historia Augusta were royals who were related to each other and also related, in one way or another, to the author of the Historia Augusta itself.
Emperor Vespasian executed C. Helvius Priscus I (husband of Fannia), and his son, C. Helvius Priscus II, was put to death by Emperor Domitian. In the Epistles and Panegyricus of Pliny The Younger, Loeb Classical Library edition, page 565, Tacitus, as C. Julius Cornutus Tertullus, was the guardian of a daughter of C. H. Priscus II (note that Tacitus was aka Neratius Priscus). Apparently, this daughter of C. H. Priscus II was still young and unmarried, however, the wife of C. H. Priscus II, was still alive (Antia/Arria Fadilla/Claudia Phoebe/Pompeia Plotina). But, under Domitian, she and the other Piso family members were banished from Rome.
The main link to Domitia Lucilla II as the mother of Pertinax is given in the Historia Augusta, where his mother's name is given as "Lucilla". The index of Pliny The Younger, Loeb Classical Library edition, and particularly, a letter on page 301 of Pliny's Epistles, provides more information regarding C. H. Priscus I, II and III.