Opinion of the Court. 270 U.S. the same cause is pending. Each court is free to proceed in its own way and in its own time, without reference to the proceedings in the other court. Whenever a judgment is rendered in one of the courts and pleaded in the other, the effect of that judgment is to be determined by the application of the principles of res judicata by the court in which the action is still pending in the orderly exercise of its jurisdiction, as it would determine any other question of fact or law arising in the progress of the case. The rule, therefore, has become generally established that where the action first brought is in personam and seeks only a personal judgment, another action for the same cause in another jurisdiction is not precluded." Kline v. Burke Constr. Co., 260 U. S. 226, 230. It is urged in behalf of respondent, that the federal act is supreme and supersedes all state laws in respect of employers' liability in interstate commerce. That is quite true; but it does not advance the solution of the point in dispute, since it is equally true that, in respect of such liability arising in intrastate commerce, the state law is supreme. Judicial power to determine the question in a case brought under a state statute is in no way inferior or subordinate to the same power in a case brought under the federal act. The Iowa proceeding was brought and determined upon the theory that Hope was engaged in intrastate commerce; the Minnesota action was brought and determined upon the opposite theory that he was engaged in interstate commerce. The point at issue was the same. That the Iowa court had jurisdiction to entertain the proceeding and decide the question under the state statute, cannot be doubted. Under the federal act, the Minnesota court had equal authority; but the Iowa judgment was first rendered. And, upon familiar principles, irrespective of which action or proceeding was first brought, it is the first final judgment rendered in one 611 . Opinion of the Court. of the courts which becomes conclusive in the other as res judicata. Boatmen's Bank v. Fritzlen, 135 Fed. 650, 667; Merritt v. American Steel-Barge Co., 79 Fed. 228, 234; Williams v. Southern Pac. Co., 54 Cal. App. 571, 575. And see Insurance Co. v. Harris, 97 U. S. 331, 336, where the rule as stated was recognized. The Iowa court, under the compensation law, in the due exercise of its jurisdiction, having adjudicated the character of the commerce in which the deceased was engaged, that matter, whether rightly decided or not, must be taken as conclusively established, so long as the judgment remains unmodified. United States v. Moser, 266 U. S. 236, 241, and cases cited. And, putting aside for the moment the question in respect of identity of parties, the judgment upon the point was none the less conclusive as res judicata because it was rendered under the state compensation law, while the action in which it was pleaded arose under the federal liability law. Dennison v. Payne, 293 Fed. 333, 341-342; Williams v. Southern Pac. Co., supra, pp. 174–175. 2. In the Iowa proceeding, the widow of the deceased was a party in her own right and clearly was bound by the judgment. The action in Minnesota, however, was brought by the administrator, and the state supreme court, on the authority of Dennison v. Payne, supra, pp. 342-343, held that there was a want of identity of parties. The decision in the Dennison case rests entirely on Troxell v. Del., Lack. & West. R. R., 227 U. S. 434. The effect of the last named case we pass for later consideration. Hope's death as the result of the negligence of the railroad company gave rise to a single cause of action, to be enforced directly by the widow, under the state law, or in the name of the personal representative, for the sole benefit of the widow, under the federal law, depending the character of the commerce in which the deceased and the company were engaged at the time of the acci upon Opinion of the Court. 270 U.S. dent. In either case, the controlling question is precisely the same, namely, Was the deceased engaged in intrastate or interstate commerce? and the right to be enforced is precisely the same, namely, the right of the widow, as sole beneficiary, to be compensated in damages for her loss. The fact that the party impleaded, under the state law, was the widow, and, under the federal law, was the personal representative, does not settle the question of identity of parties. That must be determined as a matter of substance and not of mere form. The essential consideration is that it is the right of the widow, and of no one else, which was presented and adjudicated in both courts. If a judgment in the Minnesota action in favor of the administrator had been first rendered, it does not admit of doubt that it would have been conclusive against the right of the widow to recover under the Iowa compensation law. And it follows, as a necessary corollary, that the Iowa judgment, being first, is equally conclusive against the administrator in the Minnesota action; for, if, in legal contemplation, there is identity of parties in the one situation, there must be like identity in the other. The first proposition finds support in Heckman v. United States, 224 U. S. 413, 445-446, where this court held that the United States had capacity to maintain a suit to set aside conveyances made by Indian allottees of allotted lands and that the allottees need not be joined. The defendant in that case insisted that, unless the allottees who had executed the conveyances were brought in as parties, he was in danger of being subjected to a second suit by the allottees. Answering that contention, this court said: "But if the United States, representing the owners of restricted lands, is entitled to bring a suit of this character, it must follow that the decree will bind not only the United States, but the Indians whom it represents in the litigation. This consequence is involved in the rep 611 Opinion of the Court. resentation. Kerrison v. Stewart, 93 U. S. 155, 160; Shaw v. Railroad Co., 100 U. S. 605, 611; Beals v. Ill. &c. R. R. Co., 133 U. S. 290, 295. And it could not, consistently with any principle, be tolerated that, after the United States on behalf of its wards had invoked the jurisdiction of its courts to cancel conveyances in violation of the restrictions prescribed by Congress, these wards should themselves be permitted to relitigate the question." And, conversely, in United States v. Des Moines Valley R. Co., 84 Fed. 40, where a suit in the name of the government was brought to enforce the right of a private party, it was held that a prior adverse adjudication by a state court in a suit against him personally, determining the same issues, was available as an estoppel against the government. The ground of the decision was thus stated (pp. 44-45): Inasmuch, then, as the government sues for the sole benefit of Fairchild, and for the professed purpose of reinvesting him with a title which he has lost, we are of opinion that, whether the present action be regarded as brought under the act of March 3, 1887 (24 Stat. 556, c. 376), or as brought in pursuance of its general right to sue, the government should be held estopped by the previous adjudications against the real party in interest in the state court. The subject-matter and the issue to be tried being the same in this proceeding as in the former actions, the losing party on the former trials ought not to be permitted to renew the controversy in the name of a merely nominal plaintiff, and thereby avoid the effect of the former adjudications. Southern Minnesota Railway Extension Co. v. St. Paul & S. C. R. Co., 12 U. S. App. 320, 325, 5.C. C. A. 249, and 55 Fed. 690. This doctrine was applied by this court in the case of Union Pac. Ry. Co. v. U. S., 32 U. S. App. 311, 319, 15 C. C. A. 123, and 67 Fed. 975, which was a suit brought by the United States under the act of March 3, 1887, wherein we Opinion of the Court. 270 U.S. held that the United States was bound by an estoppel which might have been invoked against the real party in interest if the suit had been brought in his name, because it appeared that the United States had no substantial interest in the controversy, and was merely a nominal plaintiff." Since the statutory authority of the administrator is to sue, not in his own right or for his own benefit or that of the estate, but in the right and for the sole benefit of the widow, the same principles are applicable, in accordance with the general rule that "whenever an action may properly be maintained or defended by a trustee in his representative capacity without joining the beneficiary, the latter is necessarily bound by the judgment." 1 Freeman on Judgments, 5th ed., § 500. Identity of parties is not a mere matter of form, but of substance. Parties nominally the same may be, in legal effect, different, Bigelow on Estoppel, 6th ed., 145; and parties nominally different may be, in legal effect, the same. Calhoun's Lessee v. Dunning, 4 Dall. 120, 121; Follansbee v. Walker, 74 Pa. St. 306, 309; In re Estate of Parks, 166 Iowa 403. 1 In the Follansbee case, a judgment against Joshua Follansbee alone was held available as an estoppel in another action brought by Walker & Follansbee for the use of Joshua. Justice Sharswood, speaking for the court, said: "The parties in that suit and in the action tried below were substantially the same. In the former, Joshua Follansbee was the legal, in the latter, he is the equitable plaintiff. The subject-matter of the two suits appeared by the record to be identical. The presumption would be upon the issues, that the merits had been passed upon in the former proceeding. Such being the case, if no technical objection appeared to have been raised upon the record to the right of Joshua Follansbee to maintain the action as legal plaintiff, the judgment in that action would be a bar to a subsequent action by him as equitable plain |