The Sadducees, the party of the High, and the Pharisees.
The first reading speaks of the Apostles getting into trouble with the Sadducees and with the party of the High Priest. On following days we will see those two groups joined by the Pharisees. Let's check back on the history of those three parties. For that we will need to go back to 967 B.C. when King David was dying.
David had sowed the seeds of sadness by taking many wives. Maacha, daughter of the king of Geshur, bore him Absalom who led a full scale revolt going him. And after Absalom's death, Maacha's second son. Adonijah, raised his own army, and began acting like David.s successor.
At that, Bashiba reproached David, asking why he was not keeping his promise of putting her son Solomon on the thrown. Then, David on his deathbed summoned the priest Zaddoc, ordering him to immediately consecrate Solomon king.
Zaddoc was sure if he anointed Solomon that Adonijah would immediately kill both him and Solomon, but out of loyalty to David he anointed Solomon king.
Surprisingly, the whole nation put up a shout of "Long live King Solomon," and Adonijah was forced to run for his life. Out of gratitude to Zaddoc, the people declared that their High Priests would always need to be direct descendants of Zaddoc.
For eight hundred years the people chose each High Priest from Zaddoc's descendants, but in 152 B.C. when the the only available descendent was terribly inadequate, the people chose Jonathan, the brother of their national hero Judah Maccabeus.
A third of the Jews were traditionalists who would not accept Jonathan. Half of those traditionalists left Jerusalem for good, becoming the Essenes who left us the Dad Sea scroll. The half of the traditionalists who stayed on called themselves "Pharisees," a name meaning "Separatists."
The men in Jonathan's family hung on to the role of High Priest down to Our Lord's time.
When Jonathan took over as high priest back in 152 B.C. a group of his buddies moved in to take over all the money interests connected with the temple. As a week joke, they called themselves descendants of Zadoc. They said something like this: "Zaddoc was high priest, and now Jonathan in his role as high priest is a descendent of Zaddoc. And we, as his party, can be called the new Zaddocites. That name morphed into Sadducees.