Samuel was the son of Elkanah and Hannah. He grew up under Eli, who was the priest at Shiloh. Samuel served a variety of roles in Israel: he was a prophet, the last Judge, and a military leader. He was widely recognized throughout the country (1 Sam 3:20). His home was in Ramah, where he headed groups of prophets.
At this time in Israel’s history, about 3000 years ago, the nation was ruled by judges who settled disputes, not kings. But the people demanded to have a king like other nations. Samuel was opposed to having a king rule over Israel because he interpreted that as an act of apostasy and a rejection of the kingship of God and he warned them that they would regret such a request. But God told Samuel anoint Saul, son of Kish, as king and so the people got what they wanted (1 Sam 8:6-22).
In time, the relationship between Saul and Samuel deteriorated and Saul took over certain functions that had belonged to a priest, not a king. Saul’s worst mistake he ever made is he disobeyed God after the battle with Amalekites.
And Samuel said, When thou wast little in thine own sight wast thou not made the head of the tribes of Israel and the LORD anointed thee king over Israel?
And the LORD sent thee on a journey and said, Go and utterly destroy the sinners the Amalekites and fight against them until they be consumed.
Wherefore then didst thou not obey the voice of the LORD, but didst fly upon the spoil and didst evil in the sight of the LORD?
And Saul said unto Samuel, Yea, I have obeyed the voice of the LORD, and have gone the way which the LORD sent me and have brought Agag the king of Amalek and have utterly destroyed the Amalekites.
But the people took of the spoil, sheep and oxen, and chief of the things which should have been utterly destroyed, to sacrifice unto the LORD thy God in Gilgal.
And Samuel said, Hath the LORD as great delight in burnt-offerings and sacrifices, as in obeying the voice of the LORD? Behold, to obey is better than sacrifice and to hearken than the fat of rams.
For rebellion is as the sin of witchcraft and stubbornness is as iniquity and idolatry. Because thou hast rejected the word of the LORD, he hath also rejected thee from being king (1 Sam 15:17-23).
God didn’t reject Saul’s kingship due to his actions, his disobedience, but the reason why Saul disobeyed, which is his selfishness and evil heart.
But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the LORD seeth not as a man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart (1 Sam 16:7).
God had Samuel anoint young David to be the next king (1 Sam 16:12-13).
King Saul grew jealous of David so he fled to flee from Saul and was given refuge by Samuel in his home in Ramah. David eventually succeeded Saul as king, but Samuel didn’t live long enough to see that.
The story of Samuel is found in the book of 1 Samuel, chapters 1-25.