Adam Jensen was born 42 BBY on the planet of Naboo. At age 2 his family was visited by Mace Windu because the Jedi Council sensed potential in him. His parents decided that it would be better for him to go with the Jedi.
Adam wasn't the absolute best of his class of Younglings but he was far from the worst. He picked up on things quickly. When it was time to become a Padawan he was chosen by Mace Windu. The same Jedi who came to get him when he was so young.
Mace was a tough teacher. And taught him with Forn VII: Vaapad of lightsaber combat. When he reached his puberty age he began to wonder if what he was taught was right. That connections shouldn't be made. He never publically mentioned his thoughts to his master. But eventually, he heard stories of the Gray Jedi and their disagreements with the council. He had met Qui-gon Jinn once when younger. And his talk of The Living Force made more sense to Adam, who also befriended Anakin Skywalker.
The two often talked about the things they disagreed on the concil with. And like Anakin, Adam too had fallen for someone. A fellow Jedi and a good friend. She however rejected him but chose not to tell the Council about it. A year before the Clone Wars Adam was Knighted and he went to Cin Drallig and passed the tests to become a Temple Guard. He served for a year. It was the start of The Clone Wars that took him off Temple Guard duty.
Two years after the start of The Clone Wars Adam passed his test and became a master. His Padawan was a boy from Mandalor named Leon. He taught the boy telepathy so that if they had to talk privately no one would know what they're saying. He taught Leon his own way. That connections really weren't as bad as the Council says. They make you work harder to protect your friends.
Adam also learned how to be a good pilot and mechanic from Anakin, and learned several Force Powers from the Coucil that normally aren't taught. Such as Force Judgment (light side version of Sith Lightning) from Master Plo Koon, and Shatterpoint from Mace Windu.
Sadly, when Order 66 was initiated, Adam was unable to save his Padawan and in a rage instead of coming out as yellow when he used Force Judgement, it was Blue. He had used Force Lightning and scrambled the brains of the troopers. Adam took Leon's body and escaped to Mandalor to give the boy a proper funeral on his home. He kept his Padawan's lightsaber to remind him of his failure.
Adam tried to cut himself off from the Force but he couldn't bring himself to do it. He would fight with Guerilla tactics against the Empire. Having to constantly run from planet to planet.