There are lots of stories that define Messi as a person. Most of them are in spanish.
One comes from keeper Mariano Andujar, around minute 7
It's in spanish though, so basically he says: " We played a couple friendlies, against Arabia & other teams. Not much people know this. In these kind of friendlies, the FA receives money. But if Messi plays, there's extra money. Well, he went on purpose to ask for that money. To share it with us. He talked to the management and said 'This part is for me'. Then he came and say 'this is for us, guys'. That's what a leader represents for the group. He won't talk about it, for sure"
Then there's a very famous journalist who always cover the matches from the field (dunno how to say it properly, he's not in the booth, he's near the benchs covering everything from there) who's called Titi Fernandez.
The journalist asks him "Has Messi ever done something to you that surprised you?". And he goes with the story: To put you in context, during the 2014 WC, which he went to cover, his daughter died in a car accident in Brazil. Obviuously he didn't finish his job. Then he organized a movement asking for justice.
"We wanted to honour Sole. She wanted to be in the WC Final, so we went there even if we didn't want to go. We made some shirts with Sole's face. Messi had a gesture with us, taking a picture holding the shirt. And then another gesture it was....well, Messi is a great guy you know. It's difficult to be Messi, but Messi is a great guy. He saved my life! We were in Venezuela During the Copa America -2007-. And some venezuelans invited me to play golf, a saturday in the morning. I had everything prepeared with my job: I arranged interviews with Heinze and Tevez. I had two transmissions with Channel 13, during that saturday. I finished playing golf, everything was calculated. But there was a crash in the highway. Traffic wasn't moving. The producers were calling me and I could do nothing. Well, what happened? It became late, Tevez and Heinze went home to take a nap. I was devastated. I said to the producers "Guys, if I can't fix this it's done. I quit". There were two transmissions and they were about the National Team!. So there was a guy called Pagano, who worked for Adidas, and He notices I'm worried. He asks me "Whats up?" I explained everything to him. Told him I needed somebody, otherwise I'm dead. He says "Well I'm chatting with Messi". So he writes to Messi about my problem and asks him if He could help. Messi was bored as hell in the bedroom. "If he pays the coke...". A truck full of Coca cola I'd give him!!. Messi came down, he was even happy. We've been together for an hour and made a great interview which covered everything!. So he said "Now you have to pay the coke". Went to the restaurant. Maracaibo, Venezuela, 3 PM. It was like 40°c, there was nobody, not even a soul in the hotel. The birds were falling down because of the heat. In the restaurant there was nobody. After five minutes they had to call security because they were trying to invade the hotel! That's why I say it's hard to be Messi."