Who is metal sonic in sonic heroes

I'm not sure how far you are in the game but as you probobly know, the last stage/level for each team is the Egg Emperor. Team Rose is the one you will probobly finish first so you will see or you have seen Team Rose defeating the Egg Emperor, the the robot dissolves into this liquid oil. Then, Froggy and Chocola jump out of it. You also hear some one talking far away. It's Metal Sonic. That voice is part of the end to another team's story... Team Sonic. If you finish Team Rose, Team Chaotix, Team Dark, and Team Sonic on the Egg Emperor, you'll find out that Dr. Eggman, for once, is not the bad guy. Truth is, is that Metal Sonic trapped Dr. Eggman in a jail cell which you find out when you finish Team Chaotix's story. You'll also unlock an extra level. Metal Madness!!!! In that level, you start out as Team Rose. You have to use Thunder Shoot at the heart of Metal Sonic. There are also level up cubes with them. You also want to use Team Blast of course. When you hit him enough times, you now play as Team Chaotix. With them there are still Level Up cubes, you still have to use Thunder Shoot and Team Blast, but, there is one more thing. You have cannons. Metal Sonic has flown up a bit and now you have to use the cannons to be at his height and then use Thunder Shoot. And again, once you've hit hime enough times, this time, you'll be playing as Team Dark. It's exactly the same this time except now, there are no Level Up Cubes. There are cannons though. Just do the same thing and when you've hit him enough times, you'll be playing as Team Sonic. Here, there are no Level Up Cubes, and No Cannons. He is leveled at the platform your on but he is farther away. If there are no cannons, how are you supposed to hit him? This is why it's the last team out of the four, the hardest. You have to use the flying guy, fly off the platform, get closer to Metal Sonic, avoid his attacks, and use Thunder Shoot. You have to do all that with out running out of your fly gauge. If you run out while your attacking Metal Sonic, and your not on the platform, your going straight down and you'll lose a life. Once you have hit him enough times, Metal Sonic gets REALLY mad. He grows tons of arms and starts flying. Dr. Eggman and all the teams know perfectly you can't deafeat him alone. You need help. Help, from the Chaos Emeralds. If you have already gotten all the Chaos Emeralds from the past levels, Great! If you haven't, exit out of story mode, go to Challenge, and click on the levels that have Chaos Emeralds in them that you have not gotten. After that, go back into story mode. You'll start at the part where Dr. Eggman tells you you cantdo it alone. This time, each of the Teams will pull out one or two Chaos Emeralds.Team Sonic gets in the middle of the cirlcle the teams and Dr. Eggman made. The seven Chaos Emeralds will strat cirlcling them and Team Sonic will start flying. They get force fields around them and Sonic, turns into... Super Sonic. Now, there is one more level to go. The Metal Overlord. Now that you are Super Sonic, you can fly. You'll be chasing Metal Overlord. Just keep after him avoiding his attacks and use Team Blast like six, seven, or maybe even eight times, and you will defeat him. He will fall on a platform and transform from Metal Overlord back to Metal Sonic. Sonic will say that was fun. He'll start running and Amy starts chasing him. She stops though. After that a video cut scene will show Sonic saying "That was a great adventure! See you next time!". Then the credits role on with Metal Sonic's Theme Song. All the Teams have a Theme Song. Team Sonic's is "We Can". Team Dark's is "This Machine". Team Rose's is "Follow Me". Team Chaotix's is "Team Chaotix". And, once you defeat Metal Overlord, you'll unlock a new story mode, Team Metal Sonic. Team Metal Sonic's Theme song is "What I'm Made Of".
That was a really big description about Metal Sonic/Metal Madness/Metal Overlord. If you want a shorter description, look here below.
Metal Sonic is a copy of Sonic the Hedgehog that Dr. Eggman made who can change himself between Metal Sonic, Metal Madness, and Metal Overlord. Dr. Eggman created him in the very first episodes of Sonic The Hedgehog called Sonic the Hedgehog.
Hope this helps!