Mikael Akerfeldt is currently the frontman and the leader of Opeth. The band was founded in 1989, surprisingly not by him, but by a currently unknown guy named David Isberg. Akerfeldt was in a band called Eruption before Opeth, but they disbanded. David promptly asked him to join them as a bassist "because their bass player couldn't play bass." He apparently liked that David had huge plans for the band, like live shows and recording a demo, and thought that he couldn't achieve those things without David.
When he went to the first rehearsal, it turned out that the other band members didn't know he was coming, including the bass player at the time. That day, the whole band was fired, and there remained just the 2 of them, with Michael as a guitarist and David as a vocalist.
When they finally got their first gig, they hired bassist Nick Döring, guitarst Andreas Dimeo, and drummer Anders Nordin. It was absolutely chaotic:
"I remember the crowd was throwing snus tobacco at David in his face. They stole his microphone stand and he walked offstage for some reason. I don't know where he went, he just disappeared for some reason and I was just standing with my back towards the crowd because Anders didn't really know the songs. I just stood there and kind of nodded to him, 'The next part is kicking in now.'
Nick and Andreas left the band right after the gig. The following year, David left. In 1992, the band consisted of Mikael Akerfeldt, Anders Nordin, Peter Lindgren, which Mikael Akerfeldt considers to be the real start of Opeth.