How do I turn off '*' in multi-line comments in Eclipse?

As mentioned in this thread, you can only do that (meaning "disabling the leading asterisks") by going to

 Preferences > Java > Code Style > Code Templates

So for example, if you modify the template for comments of a field into:

/**

 */

It will come that way (without any asterisk in the middle) when you will comment a Field.

However, it does go against the Sun convention for Java comment formatting up to jdk1.3 (update: current oracle link) (as seen also here)...
However, as noted in the comments by Amedee Van Gasse:

Starting with Javadoc 1.4, the leading asterisks are optional.

---

An even simpler way (if you only need to do that for certain comments of your codes, while keeping the other one with the standard style) is, when a multi-line comment appear like this one:

/**
 *
 */

, you can first remove the one leading asterisk, the enter your comments.
You will see no other leading asterisks are showing up at the beginning of each new line of comments.

 /**

  */

 /**
    My first line of comment
    My second line of comment
    My third line of comment
  */