Who issues warrants, and why? Why might existing shareholders not be happy about warrants being issued?

Who issues warrants, and why? Why might existing shareholders not be happy about warrants being issued? 

Find a warrant that is trading right now, and let us know what you can find out about it. What is the intrinsic value, maturity date, etc? Can you discover how it was issued?

Why might particularly aggressive investors favor warrants over stocks?